Hi,
you need to find out what IOS version and image is installed on the router. Issue "show version"
and look for the image name.
The best 2600 IOS image that supports most of the IPSec features is:
Feature set: "IP/FW/IDS PLUS IPSEC 3DES BASIC"
Image name: "c2600-ik9o3s3-mz.12.n-n"
You can use the Feature Navigator tool to find out which IOS supports which features:
www.cisco.com/go/fn (CCO logon required)