Another thought, make sure your bios is detecting the drive correctly. Older bios version may not be able to detect a 20 GB drive. If this is the case you may need to update your bios. As well, you can still run fdisk without actually partitioning your drive. If it shows that you are not using 100 % of the drive or that there are more than one partition, then Partition magic is the way to go. Very easy to use, convert your file system to fat32 and extend the partition.
Hope this helps,
Computerguy