You know how your hard drive is divided into partitions (usually a main one for your OS and then another one for other crap)? Is it possible to undo a partition, and if so, how would one go about do so?
~~~
[20:15] Irysa: I hate myself [20:15] Irysa: I made myself some curry [20:15] Irysa: and then [20:15] Irysa: I realised [20:15] Irysa: I wasn't hungry
You could always use a rescue disk/live CD and do the partitioning on that. This way you won't have the partition you are using mounted and it will probbably work. You should still back up though.
I don't know much about MS-DOS disks, but google up 'Knoppix' and you can boot up with that and partition it from Linux. However it might be confusing if you aren't familiar with Linux.