http://www.oscer.ou.edu/education.php. This is a free online class. Last year in the class, some distributed computing methods were introduced. I forgot the name. You may contact the professor to ask help. 

The slide link is http://www.oscer.ou.edu/Workshops/HighThroughputComputing/sipe_htc_20130326.pdf

That is an old and oft considered question.

In theory, yes, in fact it is possible. In practice it depends on what you are trying to do, and how it aligns with the resources available (hardware and server knowledge/skills).

The thing to realize is that you have to 2 distinct issues, cluster setup and simulation efficiency.

For cluster setup beyond having computers that are connected to each other and basic know how take a look at:

Xiaoquan's link  above,

http://www.rocksclusters.org

http://www.pelicanhpc.org  (check out there academic work and similar distros links).

  For the simulations themselves the relation between the system your running (and how) to the hardware matters, among other things in terms of latency V cycle time will effect whether there is any value in the set up. Your best bet here is to determine your system(s) to be simulated and hardware/cluster set up and ask on the appropriate mailing list -- do your homework first and they're both (Gromacs & NAMD) pleasant to work with.

And remember 'The difference between theory and practice is greater in practice than in theory."

In theory, this quote actually originated somewhere. In practice it is impossible for us to know... -- JohnClont

Yes u can setup a grid computing env in local area network, You can have Eg: 1 head node and 2 Compute nodes. If more compute nodes are added  gromacs or NAMD, Simulation (Execution) will be faster.