I have one too. No way to directly interface. You can take it apart and use an H bridge with the motors and other bits and pieces may be useful, but using as a ro ot with ARC is probably more work than it is worth.

I to bought one really cheap off of Ebay. I went through and salvaged it out, the motors and sensors and the charging/docking system that I am going to try to use with my robot :-}

I've got a couple of the original Silver Roombas too. A great collector edition but not very friendly for robot hacking since it lacks a serial interface.

And what about the 4210 And the discovery red? can be hacked?... I found them very cheap here too...

 And what about the 4210 And the discovery red? 
 can be hacked?...

Yes if they have the 2.1 firmware or OSMO hacker firmware flash