Now that you have the SPs installed, you shoud be able to go to Disk Management and format the rest of the drive, Start > Run, type:
and click OK. It will leave you with two partitions, so you'll need some third-party software to join the partitions if you want all the space on one drive.
To avoid the problem in future, use an XP CD with SP2 on it, you can create a "slipstreamed" disk with XP and SP2/3 on it if you wish, there are a number of utilities on the web to allow you to do that. click here