I just created an account on GOG.com to buy Fallout and i saw that they also gave you a number of free games. One of them is (obviously) Ultima 4: Quest of the Avatar. My only problem is I can't even start the game; I pressed every single button on my keyboard and mouse but nothing happens. Anyone know what i'm supposed to do? Thanks.

Do you get to the Ultima IV title screen? You have to press a button(any button I think) to bring up the options list which should give you 'Return to the View, Journey Onward, and Initiate New Game'. Then press i to 'Initiate New Game' for the first time. On subsequent loads, you would press j for 'Journey Onward'.

If you don't even get a title screen, you may need to run 'Graphic mode setup' in the start menu and play around with that, and/or run DOSBox as an administrator(on Windows Vista/7 at least).

I actually can't get Ultima IV to run vanilla on DosBox without crashing. I'm using xu4 to run it. It's technically a "remake" but it's basically a bit for bit remake. http://xu4.sourceforge.net/
You just have to install it into your Ultima IV directory.

You press the first letter in the line you want to choose. For example, if you want to Initiate a new game, press i.
It took me nearly 5 minutes of playing around to figure it out!

This Player reference card will help a lot:

http://www.paradroid.net/u4/refguide/refguide.html