I'm having this same problem with my iPad 1 and my PPC Mac running Leopard. Except I had to restore the iOS firmware using my girlfriend's Intel Mac. I can sync with that, but not sync at all on my main Mac, which contains all of my media. Despite the iTunes 10.5 release notes stating it supports PPC I've been told by someone that it only supports Intel using snow leopard. So....???
I couldn't even get my PPC to install iOS 5, got unknown error. Tried removing and reinstalling iTunes files and still the same. But now that I have iOS 5 on my iPad, I just want to be able to sync. And of course this is wired syncing I'm attempting. Sync isn't even available when right clicking in the devices column.
Any help would be appreciated.