Its all going to be new parts.
3 disks
1 for the OS's/program files and 2 mirror raid for data (prefer hardware raid not soft)
Don't care what size of box as long as you don't need to rack it.
1 DVD/CD RW and all that stuff.
Decent sound card external prefer with fibre optic out.
Decent graphics external.
WIFI
a few USB ports.
!!!! loads of ram.
No telly or any of that crap.
Just running through all the reviews on PCPRO.
Think first stop is going to have to be go down the local computer bits and pieces shop and see what they have about and the price. Its the number of Mobo / processor options you have which does my head in.