Fitting an Nvidia GTX 670 into a StudioXPS 8100

I want to upgrade the graphics card in my StudioXPS 8100 to the Nvidia GTX 670 from the existing Single 1GB Nvidia GeForce GTS 240. 

Questions: 

(1) Will the existing PSU need to be upgraded. I believe the 8100 shipped with a 350W PSU and that Nvidia recommend a 500W PSU min for the card but i have also read that the Dell PSU can handle the Nvidia card without replacement;

(2) If i do need to replace the PSU which PSUs will fit straight in to the 8100 box as i know Dell often have non-standard connections and sizes?; 

(3) Will the Nvidia GTX 670 plug straight in as a replacement for the existing card or will i have issues with PCI=express slot availability etc?; and

(4) any other issues that i should be aware of?

Cost not really an issue but i am not particularly computer savvy so the simpler solution the better.

Specs below:

StudioXPS 8100 : Intel Core i7 Processor 860 (2.80GHz, 8MB)

Memory : 8192MB (4x2GB) 1333MHz DDR3 Dual Channel

Hard Drive : 2TB(2x1TB) Serial ATA Raid 0 "Stripe"(7200RPM)Dual HDD

Heatsink : 95W Processor Heatsink

Graphics Card - Single 1GB Nvidia GeForce GTS 240

Many thanks,

J