Hayley,
All the ways I can think of (unless you can use those free partition managers I mentioned) need third party non-free software or access to another win2k machine, with enough space to copy your installation onto. This would involve making you drive slave in other machine. Log on too other machine with Adminstator priviledges. Copy all your C: drive to a folder on this machine's drive, apart from pagefile.sys (you can just do this using explorer - making sure hidden & system files are set to be visible in folder options, view). If any permissions problems copying from your drive, just take ownership of the problematic item and give access to current user. Once all copied, delete partitions on your drive and create one new one. Copy saved c: drive back to new partition. Put drive back in your machine - see if it boots. If it doesn't, boot from 2k install CD and select repair using recovery console (you'll need administrator password). When you get to a command prompt, type fixboot. Then type exit and boot with hard drive again. Should be ok now.
Other than that - have you a backup device (eg, cd writer), so you can backup, format & reinstall.