|I suggest that you bite the bullet and start over.|
I suggest you partition the 1TB drive into at least 3 partitions. Use the First one for WinXP. The second for your installed programs. The third for those files you have been copying.
The C partition only needs to be about 50GB. The same for the D partition. Normally I wouldn't even make them that large but with a 1TB drive, why not.
You do know that all hard drives can and probably will fail. If your bought a 1TB Seagate then it will probably fail sooner (3months) rather than later.
Anyway any data you want to keep should be backed up somewhere.
If you take my advice then disconnect the existing OS drive until you have WinXP installed. Then you can reconnect it in order to copy the files.
I also suggest imaging the C & D drives. That way if you do have a failure or need to reinstall for any reason you will have that capability. Saves a lot of time.