mesocyclone:
I usually go to the NCDC for archived radar images. Let me just point you to the general site for radar imagery (which has pretty good information on how to unarchive). Poke around, and if you have any problems, post back here and if I cna help, I will:
http://www.ncdc.noaa.gov/oa/radar/radarresources.html
The NCDC is also a place where you can get archived satellite imagery:
http://cdo.ncdc.noaa.gov/GOESBrowser/goesbrowser
There are any number of other sources for this kind of stuff. Another possibilty for satellite images is Dundee (have to register, but it's free)
http://www.sat.dundee.ac.uk/auth.html
If you are just looking for the last few days, you can always go to UCAR:
http://rap.ucar.edu/weather/
Or a HUGE archive (including radar and satellite) is available at Plymouth State:
http://vortex.plymouth.edu/u-make.html
Happy hunting!
WJS3