Multiple sources missing functionality ?

[Sedlak Anton <ased@cce.cz>]

Dear ATP team

I'm using  'POTATO' and alternativelly 'WOODY' distrib.
esp. for testing.

When I change apt 'sources.list' and run 'apt-get update'
I must wait while new Packages list is downloaded.
So when I switch back and for between distribution it takes
really a lot of time to download several megabytes of material
which was downloaded before 5 minutes.

Question: is there some way to say apt not to download
again and again 'Packages.gz' between switching of distribution
and show it where already downloaded Packages list is locally stored?

I appreciate any answer

Best regards

Sedlak Anton <ased@cce.cz>