Your scenario is very vagues but anyway. As you said you wanted to get tweets in live I would use the Streaming API with the FilteredStream.
Linvi
var fs = Stream.CreateFilteredStream(); fs.AddTrack("#myhashtag"); fs.MatchingTweetReceived += (sender, args) => { var tweet = args.Tweet; // Do whatever you want with your tweet }; fs.StartStreamMatchingAllConditions();