VPN for providing client web access on Linux VPS

I want to sell VPN to windows based clients, with the option of assigning fixed/dedicated IP to each. The client <-> VPN connection will be encrypted, and used as a secure tunnel for clients to access the internet. I need someone with experience, to set up a suitable solution for me on a Linux based (CentOS 5) VPS. Below are the requirements: 1)Solution must be very stable.. tried and true.. experience is required. 2)The client must be able to access the www through the VPN connection, and the solution must be able to hide the IP of the client, and show only the IP of the VPN server, to the websites the client visits through the VPN. 3)Solution must enable windows based clients to easily connect, preferably via existing network connection options in windows (PPTP, IPSec etc), without need to download and install client side software. 4)solution must be easy for client to configure and setup. 5)The solution must be easy to administer, giving the admin simple control over assigning/managing accounts (clients),and assigning or changing dedicated static IPs to each account as required. 5)Unless a static IP is assigned, all other clients will share one IP. 6)The solution should be easily replicated on additional VPS by the admin as required, without need for additional help. 7)The solution must be able to handle min of 30 clients simultaneously. If you have experience and can easily make this happen, let me know. Thanks in advance!