Never done this before, so I'm just guessing...
Once you're inside the msconfig utility, click on the tab that says "boot.ini"
There should be a white box with text in it.
find the [operating systems] line
there should be two strings below it
if you scroll to the right a little bit, one should say something like "Microsoft Windows XP Professional" or "Microsoft Windows XP Home"
and the other should be something like "Microsoft Windows 98"
Select the line that says "Microsoft Windows 98" and click the [[Move Up]] button.
Click Apply, then OK
Try rebooting....
I did all this from inside Windows XP Pro, and I don't have 98 installed, so I'm completely guessing, let me know.
-rock