I have been collecting serials and disks ready for a rebuild, (new MB CPU HDDs keep DVD drive FDD case).
THis AV2000 or whatever I was attacked in the last week and AVG7 stopped it dead
remember, your oem xp is NOT transferrable (legally) 
I am NOT transferring - same case, DVD and FDD 
Thats a transfer - its a significantly different system.
It may be 50:50 if it activates again, but the licence for OEMs is quite clear 
Well I have choices, reuse licence, sell me XP Pro, or Linux, rather not do the last one, I run some non Vistable software (CA-Clipper in VGA graphics mode)
Legally, you cannot reuse. I don't think its available in retail any more, I believe its still available in OEM chain.
I'm surprised that your software will run under Linux but not Windows :-/. Have you tried it under Vista compatibility mode? There is very little app software I have come across that doesn't.
Vista will likely run better than XP on decent Core2 hardware.
If I can't run my software might as well have a free O/S 
Most server class Linux distrubutions cost more than Windows Server 
How come?
Redhat, for example, is something like £400 per year per server.
So over the standard 3yr life of a server, Windows 2008 server works out much cheaper.