Note: This question was answerd on the forum few days back. Pls. search the archives in general.
To answer your question:
Yes, it is possible. No config is needed on the router (other than NAT).
See notes below from URL:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122relnt/800/rn800xi.htm
IP Security Through Network Address Translation Support
Cisco IOS Release 12.2(2)XI IP Security (IPSec) supports clients that do not use TCP wrapping or UDP wrapping. On Cisco 80-804 routers and Cisco 806 routers, this feature allows clients
that have wrapping disabled, or clients that do not support wrapping, to use IPSec. Each client creates an IPSec tunnel, and NAT translates the private IP addresses of these packets to public
IP addresses.
On the Cisco 801, 802, 803 or 804 routers, you must enter the following global configuration mode command for this feature to work:
ip nat inside source list number interface bri number overload
In this command, number refers to the source list number, and the basic rate interface number, respectively. The document at the following URL contains an example configuration: