LOGMEIN by Hamachi (
www.logmein.com).
If you do not want all the bells and whistles, but want to be able to remote control the other PC, it is
FREE.
If you wish to transfer files between your pc and the other one, either pay for LOGMEIN PRO or use Gigatribe (
www.gigatribe.com) you can use this
FREE, or pay a lifetime £14.99 to have more options.
I can recommend both.