after going through vista i wanted to uninstall now this is going to be a problem as vista is installed as dual boot and it has its own bootloader.
here are the steps
1. Backup, backup, backup
2. Reboot and Boot to your XP CD-ROM
3. Start the Recovery Console
4. Run Fixboot
5. Run Fixmbr to reset the master boot record
6. Exit the Recovery Console
7. Reboot
8. To remove the extra entry, edit the boot.ini file to remove the “Microsoft Windows Longhorn” entry.
9. Format Your Vista Partition.
10. if you have lots of data say in GBs and cannot move it elsewhere and sacrifice some time then the best solution would be to reinstall wxp back
11. backup everything as it will not let you delete vista directory
12 reinstall everything again, if the vista is not on a partition.