Use of old computers for computation.

Hi,

I am a PG student and voluntarily administering dept. comp. lab in an engineering college.

In the lab there are 7-8 old PCs. They have 512 MB RAM. And all are in working condition.

But since the systems are old, no one uses them. So I want to put them into use by some mean. But the single system is useless.

Is there any way to use them efficiently?
Can these systems in combination(I mean networking or something similar) will be used for computation ?

Or any other use which will put all the systems into job ?

I can handle MS windows as well as Linux (fedora).

Please help me to improve my lab.