Apple has taken measures to technologically limit your ability to do so. When I bought my most recent MacBook Pro it came with Lion. Because of network issues at work I could't use Lion (still can't), so I tried to put Snow Leopard in a VM (using the copy I had previously put on my now defunct MacBook Pro) but Apple and VMWare had put in technological blockers to prevent putting SL on a Lion VM or Lion on a SL VM. So, I repartitioned and copied my old MacBook over and am still living happily with SL.
I suspect there were other factors which prevented your success.
There were no measures to technologically limit one's ability to perform multiple installations from a purchased OS X install disc. You could buy two different Tiger installers and they'd checksum the same, and there were no serial numbers to be entered. It was an honor thing.
There was a restriction on VMs, but they've since eased up on that. I imagine it was because of the Hackintosh thing.
I'm reasonably confident the OS didn't actively try to detect that it was running in a VM, but VMware Fusion (and presumably other such software) would prevent you from installing the OS.
There was a relatively simple work around (a hack) that allowed you to install in a VM. I think it was as simple as touching the right path.
At the point that I was trying to solve this problem (and not getting paid as a result) I was unable to find anyone who had successfully gotten SL to run in a VMWare VM or Lion to run in a SL VM. Interestingly, I did find individuals who had Lion running in Lion VMs, but that didn't help me get back up and running.
Edited to add: You are correct, the technical restriction was on the VMWare side, but IIRC it was because of legal threats from Apple. Apparently earlier versions of VMWare would run SL without any problems, but the VMWare version I had would not not and I couldn't get a copy of the older version.
I'd forgotten that, but yes, I seem to remember reading that. Unfortunately I didn't have the server version and was already loosing money because of my down time, so I needed to get up and running with a known good system as soon as I could.
A funny thing about the family pack is that for at least one version of OS X, the only differences between the family pack and the single user version were a sticker that said "Family pack" on the front, and the price. The contents of the box were identical.
As I recall depending on what you paid you could install in on a different number of machines, but they didn't restrict you from installing it on more.
