Are the parts in the computers interchangeable? Such as if I want a top of the line nVidia GPU in my PowerMac G5 would I be able to go to best buy and get one? Or get some PNY ram to put in it?

Sorry JPT62089.

For now, the short answer is no for internal parts other than memory. If you look around, some people have managed to swap out things, but they are all hacks and not officially supported.

Memory is memory is memory, so you can source 'em from the best buy around.

When the new Intel PowerMacs come out, however, it will be a different story. Just go to http://www.apple.com/powermac/design.html and mouse over the circles on the case. You'll see that the existing PPC PowerMac has the traditional expansion slots that you'd expect in a regular PC.

Rumour has it the upcoming PowerMacs will even have four-core Woodcrest processors. If Apple sticks with the dual processor design, that will result in an eight-core behemoth!!! Bitchin!!!!

Hopefully Apple will fix that sometime... >.<

That 8-core sounds niiiiiiice I wonder how much it would be... lol

I agree that the mother board is off limits on a Mac, but there is more than just memory that you can modify. I added a maxtor hard drive (for a total of two), a Revolution 7.1 Audio card, an IO Gear USB 2 card, and AirPort card, an internal Zip drive and maxed out my memory.
This is more of the Chevy and Ford interchangeability. Both can be supped up but not with the same parts. The transmissions have different bolt patterns. Video cards have different software installed for different platforms but the edge card connections are becoming standardized.
With the coming of the Mactel you will see more, not less, of the same. I even heard that the Intel processors are socketed in the new Macs. The processor will have to have Mac programming, but soon that upgrade will be just as geeky as you want to get.

I know the CPU is upgradable, someone installed a 2GHz Core Duo on a Core Solo Mac Mini... or Core Duo, can't remember lol

I can't wait until WWDC, Leopord and possibly "ProMac"! aka more drooling to do...

Also wish me luck I am trying to get a job at Best Buy!