What could be causing this, and what can I do about it?
Oh, I don't know. The 33 opened windows is a good guess. And the solution is to not do that.
Well that response added to my knowledge by exactly 0%.
What is it about the 33 windows being open that causes it (the number changes depending on whether it is a window or a tab)? Is it a hardware issue or an XP limitation?
Although ieee488's response was a bit brusque, s/he does have a point. In all seriousness, welcome to Windows. It's been known to lock up if you have tons of windows open or tasks being performed at the same time. One of the operating system gurus might be able to give a detailed answer to your question about the 33 windows if you re-posted in the Software | Windows XP conference.
There's really no reason to have 33 IE windows open simultaneously. Aside from the fact that it doesn't have a reputation for being the most stable browser out there it can be a bit of a resource hog. There could also be a toolbar or some other kind of browser extension coming into play here. If you must use IE there's still no reason to have multiple separate windows open when IE7 has tabbed browsing. Personally I use Firefox & very rarely have more than 7-8 tabs open at a time. If you were to use a tabbed browser & avoid opening all the articles/stories at once you wouldn't have this problem.
I use tabbed browsing in IE7 also. I don't think that there is a way to open urls directly in tabs. However, I did try to find the maximum number of tabs that I could have open in a window, and there seems to be a limitation on that also---around 46 or so. The problem was not one of stability, but that XP refused to open any windows in any program.
The issue is not whether I should or shouldn't have so many windows open, but trying to understand what is causing this limitation, particularly when I have so much free memory left. If nothing else, it is a matter of intellectual curiosioty. I have googled this, and cannot find any reference to an inherent limitation of XP.
I'll repost this in the Software/XP side also as you suggested.