Just saying hello / PSU question

Hey everyone, i'm new to this board and the case/computer modding scene.  I've looked around and this is a very good site, seems like there are a lot of very knowlegable people here when it comes to matters of computers.

Anyways, I just finished putting together my first home built system.  Here are the specs...

AMD Athlon XP 2100+
Abit AT7 Motherboard
512 mb PC2700 ram
PNY GeForce 4 ti4400
80gb Seagate Barracuda IV
Addtronics 6896a full tower

So far the case has a window on the side, 1 80mm sunon up front and one in back, and a 120mm blowhole.  I've put blue led's in the power and hdd led holes, and have rigged up a fan control bus up front in an empty cdrom bay.  I should have some pictures up soon.

Right now im getting ready to buy a new powersupply bec the one i had broke.  I'm torn between a 400w and a 465w, would my comp be able to run on the 400?  Obviously i want to save money if possible, but any suggestions would be great.  

Thanks!