10.1 was a MAJOR upgrade to os X.
I believe that the only way to perform the upgrade was to use the CD. It may be able to be downloaded off of Apple's website, but it would be one huge file.
Were you upgrading from 10.0 or 10.0.4? You may want to upgrade to 10.0.4 by running software update a few times from OS 10.0. I am not certain if that will make a difference or not.
Also, you may wat to upigrade to 9.2 prior to upgrading to 10.1. Again I don't know if that will make a difference or not. I don't know anyone who went (or even attempted to go) from 10.0 to 10.1, most people I know went from 10.0.4 to 10.1
Hope that helps,