about 6 months ago my dad built a new pc, it was quite well speced (2 Gb ram, 4000 AMD 64, 2x 6600 GT's), however, he will upgrade it and give the "old" one to me (as my pc is getting slightly old, and my mums is just ancient) on the condition i find him a new pc for under £1000 that works perfectly under Linux, he likes the extra ram (in fact he will keep his ram!), and says he needs no more than a 4000 AMD 64-bit CPU, but doesnt need the SLi at all, and would like something a bit slower from ATi, can anyone help?

btw, he has the know how to build it himself