Maximum PC

To begin, I am really new to this stuff and don't know a whole lot.I am looking to start building a gaming computer. I want it to be able to run pretty much everything, BF3,skyrim, most of the big named games, but not necessarily on max or anything. The desktop I have is pretty old and does not have anything special about it, it is all stock. I am wondering if it will be worth it to start upgrading or should I buy a newer desktop and start from there?

Info of the desktop:
Microsoft Windows XP Professional version 2002 service pack 3
It currently has 57GB out of 75

Processor: Intel (R)

Other info: Pentium(R) 4CPU 1.70GHz 1.69GHz, 1.00 GB of Ram
Sorry if I did not list enough info.
If not worth building, what are some suggestions for starting a project, it will be my first time building a gaming computer and I'm pretty new at this.

not much the p4 can do anymore, so a new build would be better than throwing away your money on upgrades.

which brings up the important part, what would your budget be? and can you use any of the present machine in a new one, the case, cd/dvd drive, hard disk, and monitor, mouse, keyboard. chances are that the power supply, video card, motherboard, hard disk and memory would have to be replaced.

Thank you for your reply, I've done a lot of research and I'm just going to start from scratch. Budget isnt a problem, I just want the best gaming computer I can possibly have. I'm not going to buy everything at once, it's going to be my summer project and hope to have it done by September, if not, definatly by the time crysis 3 comes out. What do recommend? Like everything, cases, mother boards, processor, everyhing. And thank you