For a 2600XM to see an AIM-VPN/BP you need to be running at least the following code:
12.2(12), 12.2(8)T1, 12.2(11)YT, 12.3(1), 12.3(2)T
Upgrade to one of these and you should see it with a "sho cry engine accel" command.
FYI, in future, the HW/SW compatibility matrix (http://www.cisco.com/cgi-bin/front.x/Support/HWSWmatrix/hwswmatrix.cgi) will give you this information. Load it up, put in 2600XM as the product family, and the resulting list will show that the AIM requires the above SW versions. Hope that helps.