VPN Connection by client that are remote users.

I have just reinstalled SBS2003 dual Nics and ISA server. I am getting the error 800 when I try to connect the clients to the machine to gain access to files and email. Is there a white paper or something that for once and for all explans HOW TO SET THIS UP!!!!!. I have read my help files and books I bought. They all just give little or no info as to HOW step by step. Is this a microsoft conspericy to get up to pay the $247.00 to get this done. Please Help. Thank You