Hi
with you router you can try exploring different options of doing a vpn onto your lan.
You can make use of PPTP/MPPE without any additional stuffs at the client side and with the normal microsoft OS.
You can refer the below link to have some idea on the same..
http://www.cisco.com/en/US/tech/tk827/tk369/technologies_configuration_example09186a00801e51e2.shtml
The second option would be going in for vpn clients at your client sid and establishing end to end ipsec tunnel.
below link talks about the same.
http://www.cisco.com/en/US/tech/tk583/tk372/tech_configuration_examples_list.html#anchor16
On both the scenarios you need to have proper ios loaded on your router to support the required features.
regds