Remember that after disabling UAC you have to reboot for the change to take effect, otherwise you'll still be receiving prompts.
The program is obviously trying to do something it may not need, and (maybe needlessly) requesting admin rights. By default, in XP everyone is an admin unless explicitly set otherwise, and standard users don't get asked for credentials normally. Try contacting the developer and asking them about why it requires admin privileges. Like Windows itself, most UAC prompts are often due to poorly made software instead of a true requirement.