If you are using ppm3 (it looks like you are from your post) setting of the repository via the command line is much eaiser then the "old" ppm.

rep - this will print all the repositories available, which should contain both of the activestate ones by default.

rep set n - this will change to the rep that is n in the list you got from rep alone.

rep add "Name of Rep" URL - that will add new repositories to the rep list.

The documentation that comes with the latest copy of ActiveState Perl includes the PPM documentation in HTML format if you opted to install it. It covers all of this as well.
You can get the latest PPM (currently 3.0 Beta 3) at ActiveState , if you have the latest version of Perl from ActiveState you already have the latest version, you will need to run ppm3 vs. ppm to use the 3.0 beta 3 version.