NTFS Problem after removing SBS2003 from computer

We have a computer we were using as a test bed for SBS2003. After finishing our tests on SBS, we decided to replace a defective workstation with our test machine. Before wiping the hard drive, we tried installing WinXP and removing the server install. While the install seemed to work, we found that the drive reported only 1GB capacity on a 80Gb. Windows also reported 500Mb free. Any ideas why this would happen?