Just recently came across a useful website called bikehike which is at (not surprisingly): http://bikehike.co.uk/index.php
You can upload routes to this website (in various formats) and then download them directly as courses to your cycle computer. The example below shows a route I did in Summer 2012, as a tcx file. You need to go onto Course Creator from the above website (link at top of page) and then press the Load Route link (on the right hand side bottom window). See picture below:
Once the file is uploaded, a map of the route (including elevation data if desired) appears as below:
If you then choose the Save Route option, you have the choice of saving the route to your GPS device - see below.
All in all it's a very useful website for converting from one format to another and for downloading courses to your cycle computer. Well worth using.