Spencer
If the 1841 has the security bundle (and K9 in the image name usually means that it does) then it should have support for configuring an IPSec VPN. I have done IPSec VPN on 1841s and they work well. I have also done IPSec VPN on 1721s and they have worked well. Of course you would need a feature set on each router that supports IPSec VPNs. It is also advantageous to have the VPN accelerator in each of the routers but that is not a requirement.
This link should be a good one to get you started in understanding how to configure the IPSec VPN between routers:
http://www.cisco.com/en/US/tech/tk583/tk372/technologies_configuration_example09186a008009463b.shtml
HTH
Rick
HTH
Rick