can I buy games and video’s etc. on Xbox live with only a silver account?

I dont need to play games online or use any other gold account features but can I buy and play games like “Portal: Still alive” with xbox live points on the xbox live market place with a silver account ?
If I get Dead Or Alive 4 and log into Xbox Live, will the glitches be fixed?
In about a month or so I will be buying my first Xbox 360, so I’m already purchasing the video games online. A fighting game I’m looking at is Dead or Alive 4. I went to the Wikipedia: http://en.wikipedia.org/wiki/Dead_or_alive_4#Bugs_and_errors and it stated that several bugs and glitches were in the game. If i get the game and log onto Xbox Live, will a patch fix the problems at all?
When is the game Portal:still alive for the xbox live marketplace coming out?
in the xbox page it says tbd on the realease date but I have no idea what that means
Categories: xbox Tags: alive, coming, game, live, marketplace, PortalStill, xbox