Shuttle SV24, ss40g or asus terminator

[budgieboo]

First off what does 2/3 size pci slot mean, and if it is a smaller size where do i find small pci cards and how much more are they. Next I really like the Athlon processor, but how does a P3 compare, cause the sv24 is much cheaper to buy and use a p3 vs the expensive ss40g. The terminator uses a athlon but small pci slots. ANy info would be appreciated. thanks