XP Administrator Account

Hi
Was updating Incredimail and when I went to install got message saying could not install --need administrator account
This is the first time I have got that message
Cant find anywhere to setup this account --
Running a 2 computer home network and Tiny V4 firewall on the computer in question--no-one else uses either computer
Can someone help pls

Ok
After several retries finally got it installed -somehow installation files had become locked :)
Went offline and rebooted to successful install
Tks