Agreed. Get the cable and GSAK. It's very easy to up and download waypoint (cache) location information. Much better than entering it manually. Since your unit won't support downloaded maps, there is no reason to buy Mapsource. I have it so I can download detailed maps to my eTrex Legend, but, I use GSAK for downloading cache info from geocaching.com.
When you go to any of the cache pages, you'll see links to download .loc data, or on the search results page, you'll see the check boxes to the right of each cache so you can check off a number of them you are interested in and download a .loc file. When geocaching.com downloads this to your computer, just select "open" and GSAK will launch and prompt you to load them to it's database. Then under it's GPS menu, select "Send Waypoints" and, voila, all the work is done!
As for maps, at the bottom of each cache page are links to all sorts of maps. I mostly click on Rand McNally for road maps, Topozone for topographical maps, and Terraserver for aerial photographs, each comes up centered on the cache site and allows you to do some zooming. It's all available to you free.