i personally wouldn't a 64-bit and especially a ultimate 64-bit on 3GB of RAM.
I got to at least have 4GB, it might run slower than it is now..
i know you have 64-bit home now and it's got issues.
try a fresh install of that before you go up to ultimate or
clean format to ultimate and get RAM at same time - ideal..
with you current issues, do not perform the upgrade option.