Can you be more descriptive about your problem?
Both Irobots will have the same command set. So either you need to establish 2 wireless links, one to each irobot, or have a master controller on each irobot (is that what the gumstix's are doing?) with a different address; on the same wireless link. That way your PC could send out "irobot1,drive,100" and only one irobot would listen.