General :: Multiple Servers Or One Server With Multiple VMWare?

I'm looking at setting up a couple automated systems: Here are a few examples:

* Internal accounting system to download and process emails
* Public web server to visit

I could put each system on its own separate box -- for example, it's generally good practice to separate anything that external users have access to (such as a webserver) from internal processes such as accounting. Now, rather than dishing out the money for two separate servers, could I get away with just installing new instances of VMWare on the same box for each system?

To give you an idea, these are not large scale computationally sensitive systems. The accounting one is simply downloading and tallying emails, and the latter is just a webserver with maybe 5 hits per day on a good day. I could definitely pick up a new box for say $50, but I wanted to know the general practice of using VMWare on the same box versus two separate boxes.