how can i run 3 linux virtual machines without going out of physical memory
 

I am a student and have been assigned a project where we had to install fedora 6... make 3 copies and name them as server, router, and client. Next we design a program in java where in the client and server talk through the router. The problem is i am not able to run the 3 vm's together, as it says "system out of physical memory". I reduced the memory size of the vm's to 156 MB form 256 MB and also changed the msconfig.exe file and disabled some of the programs such as whether bug, messenger, firewall, but to no avail... My RAM is 512 MB.. an suggestions?

I guess the obvious answer of "Get more RAM" isn't going to help you? Honestly though, attempting to run 3 heavy distributions at the same time on only 512 MB of RAM seems like a lost cause. Maybe if you were using something less resource intensive than Fedora it wouldn't be so bad.

Also, I don't technically think this is a Linux question. Granted you are trying to run Linux in the VM, but Linux itself isn't actually giving you a problem per-se. You are trying to adjust your Windows environment to let you run the VMs, which would make it a Windows problem,

I suppose you can't just install Fedora on a spare machine and then only run two of them in the VMs?

So what happens if you change the default run level in /etc/inittab from GUI to CLI?

I assumed since it was a Java application it was GUI based, but that is a good point. If it is a console application, then he could drop X/GNOME all together and drop his RAM usage significantly.

I havemoved this to General as it's more of a Windows question than a Linux question.

The VM that's being the router certainly doesn't need a GUI. And he could probably kill off a lot of other started-on-boot services, too.

Thanks for the reply... I did try to change the /etc/inittab file but did not find any parameter for GUI. however there was something like x11 in the default run level 5 and was wondering if that refers to gui and needs to be changed. I was acually able to run the 3 vm's by reducing the memory for each to 96mb... it does reduce the system performance but works..I would definitly like to change the inittab file if you can tell me exactly where to make the change.

No, you want to change a line that will look something like

id:5:initdefault:

to

id:3:initdefault:

(ie change the 5 to a 3).

In an FC inittab, you'll find this near the top where it discussed default runlevels