just had a check and you can use V898 maps, depending on the size of your card.
as long as you back up your current config in TThome or or just a straight copy to your HD, you can't focc anything up, as you can always undo it.
it really is a case of RTFI on the site, it's what i did a while back. you'll curse a bit, slap your forehead, try a couple of different things and eventually get it to work.
you can use a 4gb SDHC card in a rider2 which should be enough for most of the world.
if it all goes pete tong, just reload the old maps!