You need to "Map Network Drive". To do this go into your network using Windows Explorer and right click on a folder that you want to share on one of the other systems on the network. Choose "map network drive". This will add a drive letter to your system and allow you to execute programs, files and access documents on computer "B" while you are on computer "A" as an example. You will have to do this on each system for the folders you want unconditional access to.
I do this my self with music files....I keep them on one of my 4 home systems but can play them over the network from any of the computers. All I did was "mapped" my MP3 folder from computer "A" on computer "B", "C" and "D". All I need to do then is open my music program and hit play.
To execute a remote program (under most circumstances for all you critics out there) Windows needs to think that the program is actually on the computer you are using. This is why you "Map" the folder or drive of another computer on your LAN...so the computer you are using thinks the program is on it's hard drive.
Hope this helps and solves your problem.