I had the error you're talking about when I installed a SB live card in my machine (hence my first guess). After a bit of hunting online I found that it could be caused by the SB dos emulation drivers, which can be started by a SBINIT command in autoexec.bat - removing that fixed it for me.
Can you take a look at Device Manager -> SBlive (whatever it is called!) -> Properties and see if DOS emulation gets enabled there? If it is then try turning it off and rebooting.
If that fails then let me know and I'll try and find the info I tracked down when I was having problems. It's out there somewhere...
