VPN PC to Cisco router

i need to make connection netween some PCs and a 2821 router. the IOS of router is suitable. i did it by using PPTP. it is working now. but the problem is that clients on my LAN can not have access to internet by that link. I mean PCs on the internet can make connection to my router thorough internet but my clients can not access internet. I think it is better to use IPSec. please help me by some sample configurations.