Budget Custom PC Purchase

Hello all,
I'm a 17 year old avid gamer both on the PC and console, I have a moderate idea of building a PC but not extensive.
My current rig is a dinosaur age dell dimension 3000, nvidia geforce 6200 graphics card (To replace the intel graphics), 2 gigs of RAM, Pentium 4 etc etc etc.

I'm looking to purchase a new desktop PC for high end gaming such as:
Battlefield:2/2142, Counter Strike:source (anything from steam basically) World of Warcraft, and hopefully many more games that will be released.  I want to run these games on higher graphics settings while still maintaining a high fps rate(my current rig on all LOW settings gets about 15-23fps on CS:S    ).  I used to be able to tolerate all the low frame rates, but now i just want to buy a new PC and enjoy my gaming experience.  All that being said, i have a few questions. 

Firstly, I was wondering what would be more effective, purchasing parts, or Buying a custom built PC, as i said before, i have some PC experience but it isn't quite extensive (I replaced my RAM, Video Card, Installed a couple wireless cards, and I've taken older PC's apartl that's about it).  I only want to spend between 800-1000$ on core parts (Mouse,Monitor,Speakers etc not included in that budget) so i was wondering if it would be more cost effective to Order parts and build my own PC, and if it was easy enough for somebody like me to do.  If so, can somebody outline everything i would need to get a PC up and running, as well as suggest High End Video/Sound cards, Processor Types, etc somewhat within my budget.  Links from newegg and other sites would be appreciated.

If the above doesn't sound feasable (excuse my atrocious spelling and grammer, i have work in 15 minutes and i'm in a bit of a rush) can somebody suggest Custom high end PC companies and certain models that would suit me well, Links are happily appreciated.  I was considering alienware but was told i was paying an extra 300$ for a sticker of an alien so i guess i'm a bit ignorant in all of these fields.  I was also informed i should wait a month or so, due to the release of the Core i5 platform and the subsequent price shifts. 

A guildmate just built a ~$1,000 pc.  Check out the thread http://www.guardianhq.com/forums/index.php?showtopic=24969&st=0

Some good info and lot's of links to products like you mentioned.

Look at the performance 1 and performance 2 pre-builds by Digital Storm.  I think they can handle well more than enough for what you're playing right now.