I know that on the Garmin 496 there is a simple method of adding a 'proximity' circle of any size you choose to any waypoint (whether aviation or user). I did have a 296 a few years back but can't remember whether it had this facility.
It was very useful, for example, when flying an IAP into Norwich recently which incorporates a 10 DME arc.
To set it up simply go to the 'Points' tab on the main menu. On the 496 you can then see two sub-tabs - one for 'User' and the other is 'Proximity'. This second tab is where you need to go. Just enter a waypoint, or city or whatever, (by selecting an existing one from the database) and then the required distance (which is the radius of the circle you require). You will then find a bright red circle on the map page around your chosen waypoint.
I am reasonably sure this works in the same way on a 296. (and to get rid of the proximity circle you simply have to delete the waypoint from the proximity tab list).
Hope that helps
Drambuster