I am working on a Dual Xeon 2.4 ghz Dell machine with a quadro in it and a gig of ram and it runs maya, photoshop, premier, shake and 10+ explorer windows etc all at the same time and still whacks out renders faster than I've ever seen!! get the dell! unless you sepcifically like macs I would go for the dell (more software better support etc etc).

But as VectorMan said DONT RUSH THE DECISION or you mite be stuck with a machine you dont like otherwise!