Cannot open more windows - plenty or free RAM!

I have a 2GB XPSP2Pro machine with 800MB RAM free but are unable to open new
windows. I believe it is because I have many windows and IE7 tabs open at
once and something has run out of memory or handles somewhere. Is there
anything I can do (besides closing some)?

Currently I have 31 windows (SSH, SQL, IE, Outook, CMD, Notepad, EXCEL,
WORD,...) of which 4 are IE that hold 20 tabs between them. Mostly doco
search results that I want to look at later.