I can suggest you the KVM hand-compiled together with QEMU.
I have seen NO performance difference according to Various Processor Benchmarks, between a native Windows-XP and one running as Virtual "Guest" System inside my Ubuntu 8.04-1. I was quite impressed to be honest.
Disadvantage when using the default emulated Cyrrus-Logic graphics-card is only 16Bit when using max resolution of 1280-1024. But you can switch to a VESA capable "Virtual" Graphics-Card (haven't tried it yet)
Use any actual Intel/AMD Processors which are capable of "Hardware-Virtualization".
I used this tutorial: http://redbrain.co.uk/?page_id=29
But actually this line:
should be rather this:
I hope this helps you a little bit.