grr @ apple. Help needed

Ok, i have an ipod touch with 2.2 installed. My dad has an ipod youch with 2.1 installed. When he first got it i used my apple ID to get him something from the app store. He got some vouchers at christmas and has opened an account. but guess what, apple havnt thought that people would want to change the ID so they never included it in the firmware :/

The only way ive found to do it is to restore the ipod completely. The only thing is i would have to download the update again which will be 2 hours :/:/ (slow internet i know)

so i guess what im asking is, where would the update be stored on the computer. I know its shift to update but i have no clue where it is stored. The file ends in .ipsw but nothing comes up with search.

Help will be appreciated :)

Just logout of the iTunes Store on your computer > Resync > Bam.

I'm not sure if 2.1 supports logging into iTunes on the actual iPod, so if not, log into iTunes with his account on the computer, sync, and bam again.