Hello All,

We've written a program to predict landslides and now we want to distribute it (for free, what's the point of research if it doesn't help people) and we need to make sure it works on a bunch of OS's. We'd like to turn 1 computer into a test bed for multiple OS's. For example we'd like to have Redhat 9.0, Fedora Core 2, Fedora Core 3, etc. on this machine (on the same physical hard drive) that we can choose between at boot time, and have them share the same ext3 partiton on which resides the /home directory, (they would also share a swap partition).

How do I do this, obviously each OS would get it's own partition but I don't know how to handle the multip "/" directory/partitions.

I'd appreciate any help you could give me.

Having one swap partition won't be a problem. Since you can only boot one OS at a time, one swap is all you need. Create the swap partition, and as you install each distro, point each one to the same swap partition to use when booted.
One /home partition could be a problem.You probably could not use the same user name in each distro. The reason is that each distro will create hidden files in the user directory, which contain config info (user preferences) for each app used. Since each distro may do things a bit differently, you'd get quite a mess if the same user name is used by more than one distro.
However, installing each distro to it's own monolithic partition would solve that problem.
Therefore, I'd suggest that you create one partition for each distro, and one swap to be used by whichever distro is booted.

testing your program on non-redhat-based distros too (such as slackware and debian) would be really nice...

also, take a look at the Linux Standard Base:

http://www.linuxbase.org/

ok can you tell me how to do this, what's a 'monolithic' compartment, and how do I get any one of multiple directories to mount at root, with the others not being mounted, when the appropriate OS is selected through grub?

Monolithic means one partition to hold the entire OS, instead of several partitions with parts of the OS installed over several partitions. So, if you plan to install three OS's, create three partitions large enough to hold each one, with room to increase in size as data accumulates.
Also, create one swap partition, equal to or greater than the amount of ram on the motherboard.
When you configure grub, each OS is listed seperately in the menu, and each will have it's own kernel information like this:

title RedHat_1
kernel (hd0,0)/vmlinuz root=/dev/hda1 vga=0x31a splash=verbose showopts
initrd (hd0,0)/initrd
splashimage /boot/grub/images/smgl-splash.xpm.gz
color black/light-gray white/red

title RedHat_2
kernel (hd0,1)/vmlinuz root=/dev/hda2 vga=0x31a splash=verbose showopts
initrd (hd0,1)/initrd
splashimage /boot/grub/images/smgl-splash.xpm.gz
color black/light-gray white/red

title RedHat_3
kernel (hd0,2)/vmlinuz root=/dev/hda3 vga=0x31a splash=verbose showopts
initrd (hd0,2)/initrd
splashimage /boot/grub/images/smgl-splash.xpm.gz
color black/light-gray white/red

With this configuration, grub would display three RedHat installations, each in it's own partition, and tell grub where the root of each partition is located. From that, grub can find /boot/grub and complete the boot process.

ok how would I tell grub where the boot partition is... what is the syntax and how do I find out the values?