You don't have the disks from your previous computer? Maybe it's just me but I've had to reinstall Windows a few times between a couple different machines so I always made sure I had a copy of XP Home on hand. Vista has *alot* of problems still, and probably shouldn't even be on new computers yet, but instead should still be in beta form cuz it's not ready. Lots of programs, like TSO apparently, are not backwards compatible....same thing happened when I upgraded computers and ended up with XP over 95 (skipped 98 and ME entirely, both YUCK!). For a long time there were some older programs that ran smooth as silk on 95 and wouldn't run at all on XP. MickeySoft really needs to get their act together, IMO.....but that's their issue, not EA's and not the devs.
If you don't have a copy of XP Home I know I've seen some on e-bay going for relatively cheap, and that was before Vista came out when most people were still using XP, so I'd imagine you might be able to find some for cheaper now than they were then.