i assume youve done all the usual - cleared temp files, cleaned the cd, virus scan, etc. it could be down to bags of holding - apparently the game dosent like to many of them.
or it could be ToB, which caused this b4 the patch.
oops, should hav read all of your post. heres more detailed instructions:
to clear temp files - go to my computer -> windows. click the show files thing at the side. shift+delete on temp, and you should gain a lot of space. windows is _terrible_ at keeping these things in order.
clean the cd - take a clean cloth and clean outward. not around the disc. that could kill it.
virus scan - if you dont have a scanner you can find online ones. there one at:
http://housecall.antivirus.com
just run it and follow the instructions.