Firstly You need to have the PCs connected through LAN, set up IP address and set VNC for remote display. For sharing files, you can use FTP or Windows file sharing (for Windows only)
For Linux ssh is the best bet, andfor VNC access vino is pretty easy for Gnome users.
And there's no way to do this without host PC admin knowing, for obvious reasons :/
i understand that the free VNC is unencrypted unlike the paid version and not advisable for access from the internet. does that mean that my desktop is more susceptible to unauthorised access from the internet? what is the risk of the free version if it s used for remote access through the internet?