How to access another computer Remote?
Some machines will ask whether you want to allow connections on the server, during the client connection, live, such that if you don't actually see it happening, it might not work.
Secondly, if you plan to connect Ubuntu and Windows 7 machines, you must select the RDP option, otherwise, eg, Ubuntu to Ubuntu connections will use VNC.
Finally, depending on how your network is set up, you might have to use host names, IPs or FQDNs. Check them all before freaking out, as this will save you some time.
As an added bonus, there is also a trick to connect remote desktop connections behind networks where port forwards are needed to connect to machines behind the entry point. For example, if you have an access point of host.domain.com and it connects to a server on the network, you can set up a port forward using SSH, and then specify the RDP or VNC post like so (in putty for RDP on WIndows 7, this would be the example):
Source: 8585 (or whatever port you want) Destination: 192.168.x.x:3389 (where x.x is your network)