normally, you use the dos command, FORMAT (search your C: drive for FORMAT.COM)
but, it used to be, if you don't partition it first, you would lose everything already on it. with the latest versions, I don't know.
Partitioning is dividing up one hard drive into two or more hard drives, which are the addressed separately.
For example, you probably have an A: drive - the floppy, a C: drive, you hard drive, and then the D: drive, the CD (or something similar. Partitioning your C: drive, say 40GB, into 2ea 20GB drives, and your C drive becomes a 20GB, your D: drive is a 20GB, your CD becomes E: drive, etc.
I always partition my main hard drive, and put all my data on my D: drive (that way, if I screw up my C: drive, my data is not gone - unless there is a real physical problem with my hard drive), and also, when I screw up I can re-format my C: drive, reinstall all my applications, and still have my data, safe.
the best bet is to buy a program called Partition Magic:
What brand is your hard drive ? Both Maxtor and Western digital have free programs that will partition(Via volumes) for you with there brand of drive.
Windows 98 does not manage large amounts of memory well. That is one of greatest arguments for updating to XP. Of course there a whole lot of reasons not too.