4870X2

I am currently using an Nvidia N9800GX2 but would like to fit a ATI 4870X2
as it seems to be a bit faster and i got the Nvidia in haste as my mobo
supports crossfire and i may wish to add an additional 4870X2 at some point.
What i need to know is, are there any difficulties in setting up a crossfire
system.

Here are my current system specs.

Gigabyte GA X48T DQ6 mobo
Intel Core 2 Quad 2.5ghz Q9300
MSI Nvidia N9800GX2
8 gig of OCZ Reaper X DDR3 PC 10666 1333mhz ram
Windows Vista Ultimate 64bit
500 gig SATA3 HDD
Coolermaster Realpower Pro 1250watt PSU