ArenaNet is giving Guild Wars players until July 31 to reserve their names for the upcoming Guild Wars 2 MMO, and instructions on how to do so have been laid out.
If you're keen on saving your character names from Guild Wars for use in the sequel, you'll need to log into your Guild Wars account. Easy enough, but why? ArenaNet is currently building their reservation list (sounds like a restaurant) and they're only going to be looking at active accounts. Simplest way to tell which accounts are active is to, well, have players log into them.
Note that your names won't be reserved forever. Shortly after Guild Wars 2 launches, unclaimed names will be freed for new Guild Wars 2 players to use.