good price motherboard/cpu bundle

[anthrax]

hi i currently have a p4 at 3gigherz , someone has asked me to get em a tower for 300 quid , so my thoughts are to just use the p4 mb and cpu and my case/memory/ , then put his harddrive in etc ,

so to get my pc up and running again - whats a good option for around say 150 less, if its really good ill go to 200.. all i need is mb/cpu, i have all rest

any 1 have any ideas , my only stipualtions r:

must be able to boot from usb in bios!!!, [360 flashing]
sli/crossfire compatible,

i will be using several different linux distros/flavour in it also i will be using it for gaming..........


thanx in advance guys