I have used one of those suckers(dimension 4600) to flash the GeForce 6200 256MB that I bought for my old PowerMac G4. :P (no flaming please, the dell was not mine)
This your card?

If so then to be perfectly honest I would suggest that you just ditch it and get something better, anything really.
That card is pure garbage.
On the other hand, I suppose it is theoretically possible that you are missing some other thing. I may well be wrong but If I remember the audio device selection menus of Audacity when using it on my desktop isn't there Direct Sound and then some other sound input/output softwarey stuff? Perhaps one got messed up in some way meaning that any apps that use the functional one work but the ones that use the other do not?
*shrug*
As I said, I may be and probably am wrong about that last bit. Not the first stuff about that card being junk though.
I might investigate further a bit later.