Hi Mark,
I have several GPS units, including an Etrex Legend. Similar to yours, but has a smaller memory (8MB).
You could load Garmin's City Select software, but it takes up HUGE amounts of memory. You won't be able to load a usable amount in only 24 MB of space. These maps would be routable. This works great in my iQue 3600, which has an external memory card. I have no space limitations with that model.
For the Legend, and your Vista, I recommend Garmin's Roads & Rec CD and the Topo set. These maps are SMALL. They are not routable. They don't have the data necessary to allow the GPS to calculate routes, but you can manually create your own (PITA). If you just select "GO TO", it'll create a rubberband line between where you are, and where you're headed. This does work, but the screen is really too small for serious navigation unless you hand it to your co-pilot. I did use this method for a while before getting the iQue, which has an easy to see display.
The good news is the software can be had a great deal. The two programs I suggested don't require a registration key. The software can be purchased from Ebay, "evaluated", then resold for about what you paid for it.
