There are other 3rd party partition managers around, and windows provides its own, called fdisk - you'll find it on the win98 startup disk. Boot the machine with the startup disk in the drive, get to the A:\ prompt, then type fdisk - and you're in.
It's very destructive, though. Really it's intended for reformatting your entire hard drive, then making new partitions. And Windows isn't terribly good :0 at recognising Linux partitions anyway. So you'll have to be very careful what you do with it, or you'll lose your working OS and all your data.
It's so long since I used fdisk - and that was to format an entire hard drive before installing an OS from scratch - that I can't guide you; I simply have no idea what it would tell you was on your drive, given that the linux partition will be in an unsupported format.
I'm sure someone else out there can help - or you could try Google searching on something like 'partition manager' or 'partitioning hard drive' or 'delete partition' or...insert whatever seems appropriate.
It's even possible Micro$oft's Knowledge Base might be helpful - perhaps more so than this board, since this question isn't very linux-y any more
(Tho' last time I used information from *that* source, if I'd done exactly what it said rather than using the grey matter, I'd have ended up in far deeper brown stuff than I was to start with...)
Slegdehammer option: If all else fails (and as long as you have a copy of your chosen OS
) - back up your data to CD or Zip or whatever you have, fdisk the entire drive, set up new partitions and reinstall windows. But if you have any non-standard device drivers on board, make sure you know where you got them from, so you can find and install them again afterward.