Most servers do not have good GPU's in them. Xeons are not very good miners either. I would go with a PC with a AMD/ATI crossfire dual/quad card combo...
AMD/ATI cards are better at mining than Nvidia Cards.
Agreed. AMD ATi 5850, 5870 to 5970, 6950, 7850, 7870 , 7970 have pretty good hashrates compared to Nvidia/CPU