I just put the RAM in the machine :). After seeing that the directory cache (I think that's the one) could grow uncontrollably I went to MS KnowledgeBase and found out about specifying a value for VCache to stop it, and that slightly improved recovery time after Poser had gone on a texture hunt, but it was OK for several weeks before I did that just as it was with 256MB. I used it that way for about six months before rebuilding with a new motherboard and switching to XP and it was much more stable than many 98 systems are reported to be. Maybe something in the driver of your video card was trying to store memory size in a buffer that held only 29 bits (I think thats 512MB is 2^29) and the extra bit for 1GB was overflowing and confusing some other parameter?