What do DSP cards do

http://www.zzounds.com/item--UADSTUPACK

Do they go inside the soundcard or something?

they provide DSP

damn jaem ur real helpful today.
anyways
dsp is:
DSP - A DSP is a microprocessor designed to work with analog signals such as video or audio that have been digitally encoded. The DSP then takes these digital representations and performs operations on them. DSPs are used in video, sound, and modem technology. Intel's MMX instruction set was the first attempt to make x86 processors (specifically the Pentium processor line) more capable of DSP operations. This follows Intel's theory of putting all the processor work onto its processors. However, DSP chips are still used in many devices for PCs, as they can keep the CPU from being bogged down.

now this means that it takes a analog signal and turns it into digital, 0's and 1's. so with dsp effects u are manipulating the audio as numbers instead of the actual freq as you would on say a analog filter. That card you posted uses what u record, the actual freq and turns it into digital signals and then runs it through different algortihms. Its an effects processor, which plugs into your audio DAW. It would be like a dedicated reverb, delay, flange, etc... Thouse are supposed to be real good cards though.Its not a soundcard though. just an effects unit for your pc.

I was gonna say they kick ass.

the simple version:

they add super-charged VST/Aus etc to your digital audi sequencer. They fit in the PCi slots in your PC/Mac. They don't use a lot of the main cpu to provide very high quality plug ins.