mmsystem007 error in windows 98

Give us more details of the problem, then only we will be able to help you to solve your problem.

This was frequently caused by some of the related files being corrupt or missing.

Have your Win 98 disk hand and run
sfc /scannow
from the Run box.

If that doesn't help, you might need to re-install.

I'll see if I can pull up the old MS KB on a TechNet CD. (This would be much later today.)

Or, search http://www.google.com/search?q=mmsystem007+error+windows+98 and see if you can find the list of files that need to be present or replaced.