Simple software to show and modify GPS tracks

Try Viking - you can download and edit your tracks, and also add OpenStreetMaps, Terraserver or DEM layers. It also allows to have georeferenced map layers and some other features.

I've found Merkaartor (in the repos) to be the simplest. But JOSM is the most used and widespread, it's a PITA to find the right version to use.

I'd say give Merkaartor a shot :)