you probably need to read up on IPSEC first, but www.freeswan.org is a good place to read about ipsec in linux. afaik ipsec is not meant as client to site, but site to site VPN, but for linux i wasn't able to find anything but IPSEC. In my humble opinion, you guys should spend 800$ and get a Netscreen 5 XP (whatever new flavor they put out). That will save you a lot of headache (especially if at this point you don't much about VPN) another easier solution is to use Astaro linux or somesuch to setup a VPN server, and also get windows clients from them.
hope this helps, ids
