I have a Q6600 system (quad core) with 4 gig of memory (3.5 gig usable), Windows XP 32 bit and could not understand why I had trouble opening more than 10 or 20 IE windows without  weird issues in the desktop.  I’d be missing portions of the UI, couldn’t bring up windows and generally things slowed to a crawl. How could that be with lots of free VM as reported by the task manager?

Well the answer is a tuning parameter that limits how much memory a given desktop application can utilize. This blog post from 2004 describes the problem in detail and has the fix! Windows XP flakiness – solved

I set my SharedSection value to 8096 and I can now open 30 IE windows with no issues. This has bugged me for months and the problem was forming a proper Google search to find this post. Thank you Kevin Dente!