Alienware x51 help please!!

First off, what is your budget? Once we have that, we can offer much better help on what to pick and what not.

To answer your question, don't expect any good gaming on that thing. The CPU is good, but the graphics leave something to be desired for sure. The problem with the X51 is its small and you will be fairly unable to upgrade it. Ever.

False, the X51 is quite upgradable to a certain extent. There are already people who have Nvidia GTX 560tis in their X51s. The thing can also hold a HD 7970. as long as the TDP for GPUs is around 150watts you should be fine.
Also to the OP here is a video of an AlienWare X51 with the same specs as the one you're buying playing Crysis 2 in 1080p DX11 maxed out.
http://www.youtube.com/watch?v=pOID2A6Tp0s
Also to the poster at that point why not just pay $50 more and get a GTX 555 in it?

I had already placed the order... So can't change it nw  

I hoped that the x51 would be upgradable so that's the main reason I bought it   and being a small factor pc I really wanted it ....

Am mostly going to be using it fr some casual gaming ( hardcore if possible )

I stand corrected then, I just watched the video where someone upgrades the GPU with a 560. Very impressive, love how the GPU takes up most of the back side of the sucker.

Yeah... i knw   but im only gettin only the 240W power supply.... im seeing if i can get a greater external power supply.... suggestions?