Can my computer run it?

Go here :
http://cyri.systemrequirementslab.com/srtest/
Select the game from the select product drop menu and click Can You Run It button.

Your computer has more than enough juice to run the older games with ease. However, that does not mean that your particular game will work on your computer. More important than computer specfications is the kind of operating system that you have on your computer. If you have Windows XP installed on your computer, it can run any games built for Windows XP. However, if you have Windows Vista on your computer, some Win Xp games will work while others won't work. I found this out when I bought a pc with Vista on it. The newer Windows 7 (to be debuted on October 22, 2009) is supposed to have resolved this compatibiltiy issue.

Yes.

You should be able to run it. The FX 5600 is kind of an old card, but the X3100 is a pretty bad card so I don't know if you'll be able to run it well. Also, playing a game with the minimum RAM is usually a bad idea.