To setup PPTP VPN on dd-wrt

In Services-> VPN-> PPTP Server:

PPTP Server: Enable
Broadcast support: Enable
Force MPPE Encryption: Enable
Server IP: 0.0.0.0
Client IP(s): 192.168.2.51-55
CHAP-Secrets: user1 * pass1 *
user2 * pass2 *

where client ip stores what IPs will be assigned to the client. In the above case, the server will assign 192.168.2.51 to 192.168.2.55. The subnet can be different to the NAT in the server (192.168.1.X)

CHAP-Secrets stores the username and password for the logins, multiple accounts are supported.

DD-WRT, my most favourite custom firmware for wireless router, released the new version 2.4 SP1.

http://www.dd-wrt.com/dd-wrtv3/index.php

If you don't know, DD-WRT is a free custom firmware for many brands of wireless routers, that add many advanced features to the router. e.g., ssh, samba, printer sharing, multiple ssid, wds, wireless bridge, traffic control...