Url Mapping with asp.net

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I'm creating a site, and i need to have my urls mapped . i want to avoid losing css during mapping. i want something like this..http://www.vitagamer.net/Game.aspx?id=12tohttp://www.vitagamer.net/games/this-is-a-game-name/now i've been thinking about the following algorithm..1) receive the requested url..2) break into parts, and search database for id associated with "this-is-a-game-name".3) serve the http://www.vitagamer.net/game.aspx?id=12 pageI've been looking on the web but i'm confused. How do I do the mapping?how many ways are there?is there a difference between rewriting and mapping?I am using c#.thank you.