VPN without fixed IP

hi there, I'm trying to build-up a VPN-Entrance over our Linux-Router (Kernel 2.4.4). Some Road-Warriors of our Company should get the ability to get access to our NT-Server with a Sysbase-DB. First of all I have to learn something about its (VPN) functions: What about DSL-VPN? Is there any chance to create a VPN without a Server-Side fixed IP-Adress? Which Documentation of VPN-Knowledge do you perfer? Thanx4help, René