How to access your computer remotely

How you choose to access your computer remotely depends on several factors. Your operating system, the type of access you need and the location of the computers.
Windows XP and Server 2000/2003
Microsoft has included a utility called Remote Desktop(RDP) which allows you to connect and operate your computer from another computer just as if you were there. Your desktop appears in a window. Click, drag and drop. Remote Desktop can be configured to use 3 encryption levels.
If you want to transfer files to and from the remote computer more than just a quick copy and paste you will have to use an additional SCP or FTP utility. WinSCP is a very nice free and full featured solution for file transfer in a windows environment.
LINUX/UNIX
Unix devices provide many built in utilities for remote access, control and transfer. FTP(file transfer protocol), SCP(secure copy) and SSH(secure shell) are usually good enough for most needs and are included in the operating system.

Secure CRT from Vandyke Software or PuTTY give you a really nice interface if you are accessing a UNIX box from a windows desktop. Secure and encrypted access to the command line is easy and they also allow for secure FTP (SFTP) transfer within the same utility.
Macintosh OS X
The Mac user has many options especially since OS X is built on a unix kernel. Utilities for remote terminal access allow FTP, SFTP and SSH. There are also remote desktop management utilities available like Remote Desktop 2.
Virtual private network (VPN)
Whenever possible and practical a VPN should be used to connect between locations, especially when connecting over the open Internet. You should never use clear text