Howdy Elvenlord. You can do this with a anolog to digital converter such as an ICL7107 or NJU9202.
See this link for an example:
Led display digital Voltmeter
Also, through my experience with creating a voltmeter, it is often cheaper to purchase a panel meter for around $12 US which commonly already contain the necessary circuitry (ADC and selectable range). I've priced the ICL7107 and the NJU9202 IC's to around $9 to $12 US...then you add on the discrete components and a PCB and your cost will often be greater than purchasing a panel meter. Plus, a panel meter is often smaller and easier to fit to a chassis or enclosure. BUT, if you're looking to learn how this all works, than creating the circuitry yourself would be a good experience.
Here is an example of the panel meter that I'm referencing:
**broken link removed**
Please keep in mind, whether you go with a panel meter, or designing a circuit yourself, the ADC cannot measure it's own power supply, thus, you'll need a seperate power supply for the meter circuit additional to the power supply that is under test.
Let me know if you have any other questions. Good luck!