Incorrectly formatted hard drive

I purchased a Western Digital 500 GB WDC500 drive and then made the
silly mistake of trying to format it with an older opsys that did not support
a large capacity drive. I decided to obtain a copy of XP Pro-SP-3 and attempted to re-format the drive. Xp now does not recognize about
400 GB of the drive. It is running o.k. but I'd still like to have access to
the rest of the drive. What are my options..? MB is an ASUS P5GC
if that helps.

 

Use the XP CD to delete all partitions. Then create the partition(s) that you desire. Having two partitions on the same drive can be a blessing, as you can store or backup your files onto the second partition or D drive. In the event you have a problem with your C drive, you can format the C to wipe it clean, and your D drive will be untouched with all files intact.
Or use the WD CD that came with the drive to do the same thing.