"which I am told is not very good"
Not a good enough reason for change, imho
Also, if the AC97 is onboard, which it more than likely is, you should be disabling it in the BIOS before you start playing around installing other sound cards
If it worked before, why change it?
As for the 'sudden' error message, it could be related to the fact that you still have your onboard sound enabled...
Jim