Tartan
I wouldnt worry too much about the power supply as I believe this would be the least of you're problems.
Have a look at some of the CFS3 forums and see what the goss is....you will find some very useful info.
For starters I would look for at least a 64mb card as a minimum...something like a Geforce 3 TI500 or if you have money to spare go for a 128mb card as mentioned previously. CFS3 is a memory hog so 512 DDR is a good start as well as a CPU upgrade is you want to run the sim without loss of frame rates.
I run a AMD Athlon XP 1800 with 512 DDR 2700 on a Geforce 3 64 mb card and still find this to be borderline,however it runs IL2 Sturmovik and MS 2002 sim quite well.
Have a look at the link below in the forums section
http://www.netwings.org/
Lozza
