Hi Biggles. Try and stretch for the new 495 model. Similar unit, but faster updates than the 296 and has a better screen.
Updates to the firmware can be loaded at any time as they are released on the Garmin website. Jeppensen (airspace) updates you need to purchase from the site as they are released, perhaps quarterly, from memory about US$40 each.
Updating is pretty easy via the USB cable. Unfortunately I haven't come across anyone that knows how to do dodgey free updates. Would be interested to hear if someone has cracked the Garmin code.