With XP up and running, you can partition and format 'unallocated' space from Control Panel>Administrative Tools>Disk Management. It will be a separate partition from the system partition, of course, but no need to get involved with any third-party software like a Linux live CD, or any of that other stuff.
Or, still without the need for any other software, if you really want to reclaim that 50Gb but don't want it to be a separate partition, boot from the XP CD,
delete the existing system partition (C:), then re-install Windows on to the 'unallocated space' which should automatically include the space you lost before.
Windows XP setup will automatically partition and format the total space as one partition before installing itself. You should have done that instead of using the Seagate utility supplied with the disk. Seagate supplies that for those still using an old version of DOS-based Windows where partitioning is more like a black art.
If you don't fancy re-installing Windows (understandable since Product Activation was foisted upon us) then, as SRX660 rightly says, Partition Magic can 'merge' the 50Gb with the existing C: drive without breaking Windows, plus you can run it within Windows using a wizard-driven interface to indicate what you require it to do.
Edited by pip22, 02 November 2006 - 12:27 PM.