Dell XPS 420 Power Supply and GTX 285?

Hi, I am an owner of a Dell XPS 420.  The desktop in question came with the 425W PSU with 2 +12V rails at 18A each.  I want to put a GTX 285 in said computer.  Will the power supply be enough?  I know Dell claims it's enough for a 260, and the 285 is only like 5 watts more TDP than the 260(65nm).  The rigs specs are below.

DVD Drive

2x 1TB WD Caviar Black HDD

Q6600

3GB's DDR2 @ 800Mhz(4 DIMM's)

8800GT(To be replaced by an GTX 285 if possible)

Thanks.