I use Mapsource for plotting routes. It's just fine. Make sure you download the latest version from Garmin - they did a whole host of improvements not so long ago.
Mapsource saves files as .gdb, you'll have to do a "Save As" to save as .gpx. Mapsource will also transfer to your Garmin and receive back the tracklogs afterwards if you are interested in them.
You can also get hold of a utility called WinGDB which converts routes to tracks and tracks to routes in a gdb file. Note - the WinGDB I have only works with version 2 gdbs; one of the Mapsource updates bumped the format version to 3 which won't work with WinGDB, but you still have the option to Save As a version 2 gdb in Mapsource.
You See... others are right to a point - GPS is basically easy, but there are many subtle nuances to trip you up and ways you could be doing things better. I've had one since last November, and I'm still learning how best to use it - and you can bet I'm using it in a different way to others.
By the way - don't send any routes to Maladict - he complains endlessly if/when they go wrong
*runs away from Maladict*