I have win7 and we have some computers in LAN.
Now i want to remotely access my friend's computer.We are developers and want remotely help each other without moving here and there.
I know these two option.Windows remote assistance, remote desktop connection.
When i connect using remote desktop connection one of computer is logged off.
There may be any other option which i may not aware of.
Since you are aware about Windows remote assistance, I think you must know how to use this service. If yes, then great; otherwise if you want some help with it then refer this Microsoft Technet article.
To access own folders is easy, just share the folders from your pc itself, then using the network drive mapping function in Windows, you can easily access the shared folders from the other pc while being connected to it
As lordt have suggested, i will recommend you Team Viewer. It is a great software. And make sure when you are connecting Lan it is secure with a password so other people cannot access and also make sure your firewall is not on. Firewall can block off the connection, disable it for the time being. See whether this helps.