Here is a URL for L2TP:http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120t/120t1/l2tpt.htmalso beware of high cpu utilization:http://www.cisco.com/warp/public/794/l2tp_highcpu.html
You can use the VPN 3.5.1 client & upgrade the IOS on the router to 12.2.8There is a url for doing this:http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t8/ftunity.htm#xtocid25