first computer im building >.< please help!

Ok so im coming here since i think this is the best pc forum out there. I was thinking about getting a pc. My two options are to either build it, or buy an inspiron 518 from dell.

For the inspiron 518:

i was gonna get the 739 model and get a separate 3870 HD

http://www.dell.com/content/produc [...] l=en&s=dhs

http://www.newegg.com/Product/Prod [...] 6814129100


But the price seems to be a bit big, seeing as i can buy a barebone kit and make a better computer for less, i was thinking about this:

http://www.tigerdirect.com/applica [...] 0-9110%20C

http://www.tigerdirect.com/applica [...] &CatId=367

http://www.tigerdirect.com/applica [...] CatId=1588




This is also my first computer build too, so please tell me if im doing everything right.

Also if you can suggest a better build that'd be nice too, i have a budget of around 700-800