adding up power

i used to know how to do this but i forgot so if someone could refresh my memory it would be great ---> how do you add up the power requirements of all your components to see how big of a power supply you need?
im gonna be getting a 1 ghz duron, 256mb ram, a 16 to 32mb geforce card or equivalent, 40 gig hard drive, winxp home, nic card, floppy and a 40x burner
you think 250 w would be too close to the edge for all of that?
thanks

Here is the PC Power and Cooling power requirements chart;
http://www.pcpowerandcooling.com/maxpc/index_cases.htm

Remember to always error on the high side. You can never have too much.