I haven't got XP, but isn't there a compatability mode? (like the old MSDOS one with 98, only with XP it's for 98) There is according to PC Gamer anyway
. Failing that, you could try using UEd v1 (the Visual Basic one), it comes with the normal, un-patched UT (so make a backup of it before patching to 436). I'd think that the only reason the INF UEd is more unstable than UT UEd, is because of the greater number of packages etc that are being loaded - it's the same program being run after all
(also you might have a problem with your memory, err RAM
, that is only showing up now that it is actually being used efficiently..)