You originally posted that you replaced the old drive due to booting problems, so it is not beyond possibility that the structureof the partition where Windows used to live, is actually damaged. That would explain the booting problems.
Have you checked this disk?
Go to Start > Run > type [b]chkdsk D:[/b] (assuming your 'old drive is now your D: drive) and see what it comes up with.
If it reports any Cluster problems just answer YES to any questions it may ask. Then do it again, only this time type [b]chkdsk D: /r /f[/b] and, if the disk has any errors, the errors will be repaired as best they can.
Although, from what you originally posted, if you have encountered boot problems sufficient to warrant the purchase of a new drive, on which you now have a fresh installation of Windows XP, quite why you would be bothered that you cannot find any content in the old-Windows partition is puzzling to me.
If your other 'data' partition remains intact, why not just format the old partition and be done with it?