It all depends on what games you are trying to run. Games such as League of Legends and Counter-Strike: Source don't need much, where games as the Call of Duty Franchise and World of Warcraft, you would want a much better PC. read more
Well, it depends on the games you want to play. You have to do a lot of research. Some games require a big graphics card, some require high processor speeds. I recommend requirementslab, its a website that tells you what you need to play a certain game. read more
Actually Steam games have higher system requirements than OnLive: all you need for OnLive is a PC of any kind with a recent internet browser, while you still need a pretty powerful PC to play most game you can download off Steam. The Steam client itself is, yes, just a very simple application, but the games are a different story. read more