Windows XP audio device disappears from audio properties, suspected .dll problem

All,

I was messing around with an old document scanner (really old, like
1999 old) and needed to download some windows 98 dll files and throw
them in my XP system directory. That's the only significant change I
made to my system.

Long story short, my audio device disappeared completely from the
sounds and audio devices properties dialog.

The device shows up on my machine.
It isn't a hardware issue, I've tried switch to onboard sound and
moving my PCI sound card to a different slot.
It isn't a driver issue.

You'll just have to take my word for it, I won't bore myself and you
with the details of my troubleshooting methods.

Dxdiag gives me:
Error: Problem getting extra sound info, result code = 0x80070057
(Invalid argument(s))

DirectSound test results: Failure at step 3 (DirectSoundCreate):
HRESULT = 0x80070057 (Invalid argument(s))

When I try to test my sound.

Again, my audio was working fine for months and then suddenly
stopped. I was hoping it was a hardware problem (since that would be
easy to fix) but it doesn't seem that is the case.

What .dll files are involved with windows audio? Anyone have any
advice on this matter?

Thanks,
Steve