ok, try this:
mount -t vfat /dev/hda3 /mnt/c/
which will mount your win98 partition. This only works if your win98 partition is fat32? if you have it as NTFS, it won't work.
The reason your command wasn't working was the option '-o rw', which means you want to write to a vfat partition, which linux will not do, and for good reason! all you can do is copy files across to your linux partition in order to modify them. If you are only reading or viewing/ listening, you can do it directly from the mount point. any other bother, post up again....