Zig, I think you're a little off (but we all knew that anyway ).
[quote:aaay0sj0]the largest limitation of any system will be the FSB speed. The RAM can only communicate with the processor as fast as the FSB. I imagine the VRAM will hold to the same limitation.[/quote:aaay0sj0]

While the front side buss is the biggest limitation (generally) of the computer it is important to note that a Video card is basically its' own computer. The video memory communicates directly with the GPU and the system memory communicates directly with the CPU. There are some situations where this isn't entirely true (shared video memory), but in its' simplest form that is how it works.

The communication with the video card is through the FSB, but the computations required to put that info on the monitor is done separately by the GPU which communicates directly with it's own RAM. In normal usage this is a pretty simple (for the GPU) process - put this color at this pixel and we'll display your browser. When you start talking about displaying games and other video intensive items it gets much more complicated - color, motion, shading, etc.

DDR = double data rate. GDDR = graphics double data rate. While they are similar GDDR operates at a higher voltage and clock speed.

Now there are quite a few cards that have GDDR on the card, but also share system memory. You can think of this like a Readyboost for graphics. A card tries to perform the computations on the GDDR, while storing lesser needed info on system RAM.

System RAM and video RAM do not have to be the same type.
There are quite a few specs for video cards. If you aren't trying to run the worlds toughest games then price is usually the deciding factor. I usually look for the following qualities:
Interface - gotta have one that fits your motherboard.
Outputs - does it connect to the displays you want it to.
Core clock - the speed of the GPU
Amount of video memory on the board - As Ziggie said more is better. More memory on the card is better.
Memory interface - higher is better. 128bit provides a bigger pipe than 64bit, etc.
Memory speed - GDDR5 is faster and uses less electricity than GDDR2.
Memory clock.

If you aren't a gamer, looking for the last frame of video you can eek out of a card, set a price point and and find a card that has the highest specs in the order above - Fastest processor, most memory, higher bit interface, fastest memory.

Either way, read the specs for the card. Often they will advertise a card as 512MB, when in fact it only has 256MB on board and uses the other from system memory.

I hope that is clear as mud!

If you are a gamer your on your own! Then you have to worry about streams and shaders and a bunch of other stuff.

If games aren't a priority you can find very good cards in the $50 range. Probably not worth playing the extra $100!