I know that my husband upgraded our HD and changed one of the buttons to jump further, but I made him change that one back. Oh yeah, it was the back 5 seconds button he changed to forward 30 seconds. I like being able to say "What did he say" and hit the jump back button instead of jumping through commercials.
He used the TivoFAQ listed above and help with the software needed for the HD from some guy on the Tivo Forum.