The only experience I have with SLI is a couple of Voodoo 2's which run perfectly on a P3 setup.

Ctulu, if you're at all nervous about building yourself, buying a mobo 'bundle' is a good idea. The CPU, cooler and ram are fitted for you and tested for compatibility before being shipped for peace of mind. The rest is fairly straightforward. I used to use an anti static wrist strap to avoid any serious damage from static, which is not a bad idea.
Yesterday I finished building an AMD system for a customer:
GIGABYTE GA-MA770T-UD3
Phenom x4 955
G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666)
Saikano 650W Eco Shizen Series - PFC Activo 49Amp 12V ( I wish now it was modular)
XFX HD-577A-ZHFC Radeon HD 5770 (Juniper XT) 1GB 128-bit GDDR5 PCI Express 2.0 x16 HDCP
Case Saikano X-22 Plus c/ side window ATX Premium Fans 140mm Red/Black
The total was around 730 euros over here, but it would certainly be cheaper in Europe, so this figure probably doesn't mean a lot.
The only problem I've had so far was one dead memory card and my supplier was over to my shop within the hour to replace the memory with Corsair. That's good service.
And I agree with everyone else; a high end system needs a good power supply, no question about it. I have to fit cheapies for regular PSU failures due to the cost.
We're all different, but I must admit that I really get a buzz of satisfaction from building them and then pressing the big red button.
Couple of pics to colur up the thread:


In spite of having 2 side fans, one front and one rear, it's pretty damned quiet. The IDE cable looks out of place though.