Rats, wish I would've spotted this thread a few days earlier. I've been a Network Administrator for the past 7 yrs. & a computer field tech for 26 yrs. before that. I've worked on everything from IBM mainframes to PC's & laptops. ****, Sun, Qantel & other stuff no one else has probably ever heard of.
JHM, all the above are valid points but remember the majority of applications out there do not use quad or even dual processor threads. Not even today with multi-core processors being out for the past several years! The number of processors on any core are only good if the application you're using can utilize them. Same goes for 64 bit.
I love 64 bit ops., near endless memory & speed that can't be beat. We have 4 servers that are presently running 64 bit & they just sing.
But.....
There aren't a whole lot of applications out there that can use all that. The computer world keeps waiting for the application developers to catch-up but nothing happens overnight!
I've never been a big fan of getting sold something I don't need hence my views on multicore processors. Since you plan on keeping the computer for a few years let's hope the developers start working on the demand!

Like Apkano, I'm not a big fan of Dell, lean towards HP instead, but one manufacturer is much like any other. Hope it works out for you!!