Dell Dimension 4400 help me upgrade from outdate junk to gaming system

Hello, I want to make this computer capable of playing Crysis, Gears Of War, Call of Duty World At War, Far Cry or Fall Out on at least mid settings (or a little lower). The kid in this video plays Crysis on mid high settings with a Pentium 4 processor, a Radeon HD 3850 512Mb AGP video card and 1GB of ram(it says so in the information box on the right of the video).

http://www.youtube.com/watch?v=Z1J [...] re=related

He also plays Assasins creed on these specs

http://www.youtube.com/watch?v=Eml [...] annel_page


These are about the same specs my computer is possible of having. I'm just doing this for fun, I like tweaking old pc's to it's best possible performance to see if they can work with todays games (a weird hobby I know lol it's just something me and my friends do). The Pc has a socket 478 cpu with intel(R) Pentium (R) 4 CPU 1.60 GHz in there right now, 512mb ram (Max 1gb) and I want to throw in a Radeon HD 3850 512Mb AGP (people say this video card revives AGP motherboards so why not). What do you suggest I do to power this computer to it's most powerful performance. I dont want to buy a new motherboard since it ruins the fun. Is there any better Cpu's for this motherboard (maybe a dual core? Lol maybe..not) I just need any kind of advice on making this best thanks.