Just to be clear before you go to the trouble of downloading the client: Posterous will ban your IP for a day if you do this. The bans happen at 50 minutes past the hour, so for example at 11:50 all the bots caught downloading since 10:50 will be banned for a day.

Edit: on the other hand, the client is good for more than just Posterous, so you might as well get it anyway :)

Edit2: OK if the tracker itself is down, you can get the client here https://archive.org/details/archiveteam-warrior