Question : Problem: What is the easiest way to establish a connection to an server on an LAN from a remote computer?

What is the easiest way to establish a connection to an server on an LAN from a remote computer?

Access to the internet is from ADSL modems.

Answer : Problem: What is the easiest way to establish a connection to an server on an LAN from a remote computer?

You can setup port forwarding on some ADSL modems, check if your modem supports it.

Example:(assuming your LAN is in range of 192.168.164.x)
Forward all traffic to port 80 to 192.168.164.X:80 -HTTP
Forward all traffic to port 21 to 192.168.164..x:21-FTP
Forward all traffic to port 3389 to 192.168.164..x:3389-Remote desktop

A good guide can be found here:
http://kbserver.netgear.com/kb_web_files/N101145.asp
About Port forwarding:
http://www.simonzone.com/software/guidedog/manual/whatisportforwarding.html