Not sure what wattage to buy! Help please! First Build

Ok, I've finally got sick and tired of my mom's Gayway... er I mean Gateway. Sure on paper it's a pretty powerfull computer, but I guess I just run it to hard. Anyway, I decided to build my own. This is my first build and I'm confused about many things but they are starting to make sense as I research more. The only thing I can't figure out is what would be the appropriate wattage for my components. So far, I think I'm going to go with an ASUS A8N-SLI Premium ATX AMD motherboard, eVGA Geforce 7800GT 256-P2-N517-AX video card, and an AMD Athlon 64 4000+ so far. I don't know how much power is enough. I'm not going to run the craziest, most powerful rig on the planet so I dont plan on having a lot of extras except for some cold cathodes, a DVD writer drive, a DVD reader drive, and a lighting controller.

I would appreciate some advice on the components I have selected and ones I havent gotten to yet (soundcard, gaming mouse, etc.). Basically I'm building this computer to easily run World of Warcraft, Battlefield 2, and possibly Counterstrike: Source. Thank you

this is when it gets more complicated, when you learn that Wattage actually doesnt matter but the Amperage on each line does. a 350w PSU with 12amps on a 12volt is better than a 500w with only 6amps on the 12volt line 8O .

but dont worry bout that all good named brands like Antec, Enermax, Tagen, OCZ, will supply sufficent power.