You mentioned Windows98SE and if so then hda1 probably is a FAT32 filesystem of which Knoppix has no problem both reading & writing. It is only NTFS used in WinNT/2000/XP/2003 that Knoppix has difficulties with.

So you should find on your Knoppix desktop a icon from hda1 & if you right click and go the properties, it has a devices section which has a "read-only" check box. Uncheck that check box & now file can be written to hda1.
If you have futher questions, please ask.
I hope this helps.
James