Actually you can repartition it but you need a program like Partition Magic. Win2K's Disk Management won't resize an existing partition, only delete it. Be warned that you should backup your data, or make a Ghost image of the drive first. Usually Partition Magic works fine but if anything glitches during the repartition, or you lose power, your partition will be trashed.
With Partition Magic you could resize that partition smaller and then make new partitions.
How practical this is depends a lot on how you work and how much is already installed.
There are some real good reasons why you should use several small partitions instead of one or two big ones: damage control, ease of backup, ease of repair.
Although there's nothing that will save your data if you suffer a massive hard drive crash, most disk corruption is usually a soft corruption of the FAT (File Allocation Table). If you have one big partition then a trashed FAT will put all your data at risk. By segregating everything into smaller partitions, you limit the damage to only the one partition that suffered the FAT damage - it won't affect any others as long as it's not a physical disk crash.
Another benefit is it's a hell of a lot faster to scandisk and defrag smaller partitions.
If you work with editing video, it's a good idea to make a big empty partition just for storing AVIs you're editing. When you're done with the project, instead of defragging the drive you just delete all the files off of the video partition (no need to defrag an empty drive) and you're ready for the next project.
You can also segregate your data to make backups easier.
Here's how my system is partitioned:
I have Win98 and Win2K each in their own partitions. Nothing else is installed in these partitions. I don't use 98 except as an emergency backup for Win2K.
All my apps are installed in the App1 or App2 partitions.
Games go in one of the two game partitions.
The Temp partition is for downloads, IE & netscape cache, etc.
The smaller 1Gb Scratch partition is for temp storage of files to be burned on a Cd-R, and the larger Scratch partition is for video editing and storing large temp files like Ghost images.
All my data (and I mean EVERYTHING) is located on the data partition: Documents folder, client web pages, favorites folder, Outlook user files & address book, and any data files from apps that don't use the My Documents folder. This makes it obscenely easy to backup my data weekly - I just Ghost the whole data partition.
Every month I Ghost my Win2K and 98 partitions. I carry these, the latest data image, my Win2K install CD as well as CD-R copies of all the important apps I need in a small CD valise in my briefcase. In an emergency I can be up and running on another computer in an hour or two. It's saved my bacon twice already.