ok first thing first Remote desktop only works if the other computer has Windows XP proffessional. Telnet requires you to turn on the telnet service on that computer and Telnet is very unsafe unless you want full command line control of that computer in which case it would be used to use a vpn connection as well. Ftp Requires a FTP service to be running on the remote computer. Which can be done if you have proffessional using IIS. Although through all cases you will have to reconfigure the remote computers firewall to allow you in on your desired port. which I suggest you change the ftp port for the sake of computer safety if you chose to use the ftp service.
ok to setup the ftp service on the remote computer. download something like http://www.cerberusftp.com/
on it and install, afterwards if you have sp2 installed then you will just need to go to your firewall properties and go to exceptions then add a port name it ftp and make it a tcp 21 and thats it now anyone can see into the files you allow the service to see from any place that has a internet connection and they know the ip. another thing you will need to do is inside the gui of that server on the remote computer is setup a username and password that username will what keep hackers from screwing with the files when they portscan that computer and they will most likely be scanning it.