Upgrading basic setup

So im going to buy my first mac on boxing day and i have a few questions regarding upgrading. Im going to get the basic setup with RAM, GFX, HDD etc and the top option for the CPU as i can get components prett cheap

I understand upgrading a Mac is a bit like upgrading a PC? As in they take the same type SATAII HDD's, PCi-e GFX cards and RAM type (anyone know what socket RAM the MAC PRO Takes)

Another thing is running an ATi and a Geforce GFX card along side eachother. Does this have any negative effects? is it better to run both ATi or both Geforce?

Thanks

Joe

You may find some issues with PCI-e card compatibility, mostly to do with drivers. You're better off making sure a card specifies that it is MacOSX compatible.

As for Memory, Apples Tech Spec page says:

Memory

* 667MHz DDR2 ECC fully-buffered DIMM (FB-DIMM) memory
* Eight FB-DIMM slots on two memory riser cards (4 slots per card) supporting up to 16GB of main memory
* Up to 256-bit wide memory architecture

thanks for the response, im thinking of going for two Geforce 8800 GTX 768MB cards and some corsair RAM and a 500GB 16MB cache Seagate SATAII HDD

by doing these upgrades myself will this affect my warrenty?