Jimp,
1) Get rid of Win 98 go to Win NT or 2000 (if possible)
I haven't switched SP yet, because I was at SP2 and I had a lot of problems. So I suggest for you to go back to SP0 and wait tell someone has some good luck with a one of there new SP.
FYI - I hope you are not tring to open the same Large assembly with SW00 that you opened in SW01. If you saved it 01 you cannot reopen it in 00.
Did you set your Virtual memory to 3-4 times your Ram?
Also, what are your hardware specs?
Cheers,
Scott Baugh, CSWP