How did you install XP? Did you format the drive first? If not, your files are likely still there, just look at the C drive for your old user directory.
If you did format, remove the hard drive, install it as a secondary in another system and install and run Recuva
https://www.piriform.com/recuva see if it can pick up anything.
If you formatted, then installed things, it's likely your data will not be recoverable since the new files from XP would have over-written your old stuff. The more you use a drive where you want to restore files from, the less chance there is of getting anything out of it.