Hi,
Here is a good documentation explain AH and ESP, also the difference between tunnel mode and transport mode:
http://www.cisco.com/warp/public/cc/techno/protocol/ipsecur/ipsec/prodlit/dplip_in.htm
Here is a basic one with config explaination:
http://www.cisco.com/warp/customer/105/IPSECpart1.html
The command to choose AH, ESP and mode is in the "crypto transform-set"
crypto ipsec transform-set MamaBear ah-md5-hmac esp-des mode
Please check above links for more details.
Best Regards,