gem update --system returns error

Hi guys,

First off, I am completely new to programming and hence obviously also
to both Ruby and RoR. Please do bare with me. Yoroshiku onegaishimasu!

I am having trouble understanding what to do when the following error
appears when I try to update RubyGems:

C:\InstantRails\rails_apps\gem update -- system
Updating RubyGems...
ERROR: While executing gem ... (Gem::RemoteSourceException)
    HTTP Response 302 fetching

I am using instructions as composed by Patrick Lenz in Simply Rails 2.
I'm on Windows Vista SP1.

Thanks in advance!