It's unlikely the installer actually did what you said - I suspect something was wrong to start with.
First what XP is this....I hope that it's SP3...? If it's less than that then it needs updating urgently. There is help with that here:
http://community.mcafee.com/showthread.php?t=220807Uninstall Java from Add/Remove Programs in the Control Panel.
Download the latest from
http://java.com/en/download/index.jspWhile in the Control Panel also enable Windows Firewall.
Uninstall McAfee if listed.
Go to Internet Explorer Tools/Internet Options/Advanced and click Reset, then click Apply and OK and exit.
Reopen IE8 and re-enable the add-ons under Tools/Manage Add-ons.
Run the MCPR removal linked in my signature and reboot.
Reinstall McAfee from your account at the website.