Using VMware Workstation, the first trick is to avoid the automatic install. This is a great user-friendly feature that bypasses a bunch of normal configuration steps, but sadly, bypasses the point where you want to select the low-memory option. Thus, you need to skip specifying the .iso file when you create the VM.
After creating the VM, now go back and edit the CD-ROM settings to point the .iso and power on. You'll get the following standard splash screen for Ubuntu installs:
This just selects your language. Hit return to go to the main menu. Notice the "F4 Modes" down at the bottom of the screen. Type the F4 key, and it'll pop up a little textbox allowing you to select which kind of install you want:
Instead of "Normal" select "Install a minimal virtual machine". As far as I can tell, this has little to do with being a virtual machine. Instead, what this option means is "use the least RAM possible", as well as " reduce disk usage".
Below are two screenshots contrasting between "mini" and "full" installation. The mini installation uses 680-megabytes of drive space, whereas the full installation uses 1.1-gigabytes of drive space. In other words, the minimal installation uses roughly half the disk space. I've made them real small to avoid wasting space, so click on them if you want to actually look at them.
The changes in memory usage are more dramatic. Again, I'm including two pictures contrasting the minimal installation and the full installation. The mini installation takes 51-megabytes. The full installation takes 561-megabytes. This is a 10:1 difference! That means you can fit 10 virtual machines on a system like ESXi with the same amount of RAM as it one full machine.
The advantage of this is that you no longer need to put all your eggs into one basket. A common task for cybersec folks is too install lots of crazy software onto a single machine. This quickly breaks down as different software requires different libraries. I just messed up my BackTrack 5 VM because to install the Ubertooth One (bluetooth tool and 2.4-GHz spectrium analyzer), I had to uninstall the default python software and install a different version of python.
With smaller virtual machines, no longer have to worry. I can install a new virtual machine for every task. I can clone a base VM and install Ubertooth One on it and not have to worry that I'm screwing up some other software package.
I'm sure this is old news to a lot of you, but since I spend most my time coding rather than sysadmining, these basic sort of things are new to me.