Save your money until you can get a good pair of speakers, especially for the front. I got a pair of JL Audio xr525-cxi component speakers. These babies are awesome!!! They may run about $250-300, but they are worth it.
After you got the speakers get a sub and amp combo.
You can get great deals for $200 to 300 or less on ebay!!
For the most part you'll have a kick ass system. They only thing I would add after is a "good" quality amp (JL e2150 series) NOW you'll have the best damn ass kicken system around.
lastly, if you buy the system in steps ( like most of us do) think the of big picture on how you want to end up.