I've been receiving technical help for an issue detailed in this thread.

After the last step, when I tried to follow this:

Click Start, Run and type REGEDIT. This starts the Registry Editor. Navigate to:

HKEY_LOCAL_MACHINE
\SOFTWARE
\Microsoft
\Windows
\CurrentVersion
\Uninstall
\<Program Name>

I found that I don't have an Uninstall folder/directory. Is there a way to repair this, or is it easier to format the drive and reinstall Windows XP?

What programs did you recently install/uninstall? Try pressing Start > Run> then enter appwiz.cpl into the dialog box. Do you get any error messages when running the add/remove programs applet?

If you need something to uninstall programs temporarily I suggest you download and install CCleaner. Once you have opened the program you can remove software using the uninstall tab, located on the left hand side of the application window.

I found how one user solved it themselves, however I do not have any experience in doing any similar process, so I hope an expert can guide you through :
If all that fails I would suggest trying a repair of XP. See this article here on how to do it.

I would try almost ANYTHING before I would be willing to re-install XP. Remember that all your program settings for anything you installed after the OS was installed will be missing. Some of it will be minor and will repair itself once you run the program again. On the other hand, programs that write an encoded key of some sort under HKLM will probably need to be reinstalled, although you might get by with just re-enterring the registration key. Companies and people who make their living from software development, want to make it difficult to either move a program from one machine to another, or to have the same program on more than one machine when you only purchased one license.

The idea to try add/remove programs from either start/run or from the applet within control panel seems like a reasonible test. If you have something like MS Office installed and add/remove programs doesn't see it, that's a big problem. I would try creating the reg key by hand before reinstaqlling the OS. Unless, of course, you have a very recent backup of the entire drive that you could use to put everything back right. On my important machines, I periodically take a snapshot of the boot drive using "Ghost". I use that because I have it and it is licensed. There are other programs that do the same thing. They basically make a sector by sector copy of the drive you specify, leaving you with either one or several files that could be restored (if needed), rendering your machine back to the state it was in when you took the snapshot.

That info might be helpful going forward, but probably won't help you much right now. If you are still having a problem, let me know and I'll check my own registry for that key and see if there is anything else you need to do besides put the program name under the key. Knowing MS, I would suspect that there is but since I'm kind of jumping in the middle here, for all I know your problem may have already been solved.

Thanks,
Mike

That brings up the add/remove program window, but the only programs on the whole list I have buttons for are: HiJack This, Malarebytes' Anti-Malware, and Warcraft III. (This is no change from when I first realized I had this issue.)

The oldest system restore point I am able to get to work is from 1 week ago (11 July 08). It won't let me go to June (or change the month, period) to see if any are available.

Have a look at this article; it lists a number of possible causes and solutions:

Add/Remove Programs tool displays installed programs incorrectly