I don't know " xp x64 " watermark removing..............
U can remove watermark on Vista RC2 or build 6000 (RTM).
1. Navigate in Explorer to: "C:\Windows\System32\en-US\user32.dll.mui"
2. Take ownership of that file.
3. Copy the file above into the same folder as the original
4. Rename the original file to: "user32.dll.mui-old"
5. Rename copied version of the file to: "user32.dll.mui"
6. Download Resource Hacker
7. Run Resource Hacker
8. Open the following file in Resource Hacker: "C:\Windows\System32\en-US\user32.dll.mui"
9. Extend The String Table "+"
10. Extend the "+" next to "45"
11. Select 1033
12. Find the following lines:
715, "%wsWindows %ws"
716, "%ws Build %ws"
717, "Evaluation copy."
13. Delete or modify the lines to your liking.
14. Save the modified file.
15. Have fun, without the Watermark (or with the edited watermark)
Try to Google it, u may find solutions!