1) Validate the idea. This is very easy to do thanks to the new lean startup concept. You want to make sure that YOUR idea, the solution you're providing to a problem is turning heads. Dropbox did a great job at this(here's a clip of Drew's presentation at the lean startup conference: http://en.justin.tv/startuplessonslearned/b/262672510).
2) Make the MVP, launch it, show it to customers/users. If you feel that you're onto something proceed to step 3.
3) Take the money, dont use it unless you really have to. You want to be really ravenous and not do crazy things with it which is really hard when you get 150k+. Perhaps the best thing to do is hire someone once you really need them, I'd probably only spend that money on employees.
Good luck with your venture!