MB-G26 --- an amazing set of posts, THANK YOU. You know far more Windows "tricks" than I do, that's for sure.
However, I have one additional suggestion. A "limited" account cannot (so far as I know) perform installations. So for a Windows box that MUST cruise the Internet, I recommend performing installations with an Administrator account (what all users / accounts are by default), then setting up a Limited one and DOING ALL INTERNET SURFING with it (Firefox, Opera, whatever, anything but Internet Explorer). This will prevent "surprise" installations (because the limited user doesn't have this power to install anything).
To set up such, do [Start] [Control Panel] [User Accounts], and add a new one. There will be a non-default (as in, you must select this manually) "Limited" radio button, pick that.
And once you've done this, be SURE to password every other account on the box (including booting into F8 Safe Mode, and installing a password on the account named "Administrator", every WinXP installation has one of those).
P.S. This _isn't_ the way I do things. I may need Windows for some things, but not for the Internet. And both IE & WinXP are so full of holes (known and _unknown_) that I don't think we'll ever see a trustworthy XP (witness the recent discovery by Steve Gibson of a "backdoor" that dates back to Win98 days). We might see such in the upcoming Vista, but mainly as a dependence upon a hardware solution (which will have its own major implications for Digital Right Management, as in that CD / DVD in your drive belongs to The Corporation, not you...).
So here's an _extensive_ alternative (for the *advanced*, except that you don't need to be as advanced as MB-G26 already is
) that turns a system into a "dual-boot" one (you're booted off of Windows, or you're booted off of something else, Linux here, but only one at a time). This makes _my_ system (what I'm using right now) as safe as I can manage (and note I'm giving the Big Picture, there are MANY steps along the way, contact me if you want to discuss any of it).
Also note that this pretty much requires DSL or Cable Modem, external boxes that one connects to with an Ethernet cable. Don't blame me, years ago Microsoft took over the standard modems; part of the vast majority of "modems" are hardware, with the rest software, drivers in the OS, _etc._. AFAIK, the software emulations (many, different manufacturers) have proven difficult, troublesome, and generally not worth the trouble of the Linux community to reverse engineer, so Linux won't talk to most modems.
 Make backups (you already do this, right???). This recreates your computer, loses most everything, you must be prepared....
 Download & burn (or buy, not that many $$$) the ISOs for your favorite Linux (I like SuSE myself, it does something very important for me --- it allows a boot from floppy!).
 Disconnect any cabling (Ethernet to DSL modem) that puts your box on the Internet. Then install Windows XP. Be reasonable about diskspace, as you'll need four partitions (they may, however, be on different drives, or on the same drive):
[a] A reasonable size for the Windows partition, say 20_GB or better, but leave 10-30_GB for Linux. This will be NTFS by default (the kind of filesystem), your "C:" drive; keep it that way (XP *likes* NTFS).
[b] A second partition for "intermediate" storage. Set this one up to 1-to-5-to-10_GB, whatever. Don't format it (this will be D: down the road).
[c] Leave untouched that 10-30_GB for Linux (no partitions).
 When you're up and running off of XP, format that unused partition to FAT32 (it'll be too big for FAT, and I'm not convinced that all Linux distributions understand how to _write_ to NTFS, thus the admonition to create this intermediate partition).
 Do [Start] then right-click on [My Computer], left on [Properties], tab [Hardware], button [Device Manager], click the "+" in front of "Network adapters", right-click on your LAN card, and select "Disable". This prevents Windows from using the LAN card to get to your DSL modem (cable modem, whatever), and isolates Windows from the Internet. Without this step, you're no better off than before.
 NOW, install Linux:
[a] Let it consume the unpartitioned diskspace.
[b] If you're comfortable with whatever advanced partitioning the installation user interface offers, flag the main Windows partition as "read-only" (so Linux won't allow writes to it), or even "don't mount at boot" (so it's not even visible).
[c] Leave the default settings for the intermediate (FAT32) partition (and Linux, which has no problems with either FAT or FAT32, will happily allow you to copy files there, which you may then access by booting Windows later on).
[d] IMPORTANT: You should be able to specify a place where the boot loader goes. I'm not entirely convinced that Linux "plays" with Windows, but you're welcome to experiment (and then you want to use the boot loader called GRUB, modify the Windows "boot drive"). What I use instead is to place the boot loader called LILO onto a blank floppy (and skip the offer to put a filesystem on the floppy, I've had problems down that road).
 And once you're up on Linux, create a spare floppy or two by running (as root):
This will stamp the previously formatted and writeable floppy in the drive with LILO, which will enable it to boot Linux next time. Remember, no floppy, Linux _LOST_, no further access (that I know of anyway), so you want some spares.
When both installations are complete, you'll have a Windows XP that you boot normally, and a Linux install that you boot by inserting your magic boot floppy into the drive and booting from it (so enable "boot from floppy" ahead of "boot from hard drive" in the BIOS). And each will have read/write access to that intermediate partition, so that files may be shared between OS's.
Normal use of Linux will use the LAN card to get to your broadband modem and out into the wide Internet (and every account but for "root" is a limited account, no way will viruses have a hold on your box). Normal use of Windows will _not_, it will then be a "standalone" box, as safe as possible.
My apologies, this glosses over _many_ details, and barely scratches the surface of the wonderful operating system known as Linux (_e.g._ there's only one "look" to Windows, but SuSE has two main ones, and a host of older more primative "window managers").
Any who try this, Abandon Hope All Yee Who Enter Here, no wait, I mean "Good Luck" (and write me if you need to, I may or may not be able to "crack" problems, but I can hopefully advise where to check next