i dont know how big to get is 350w gonna be enought?
im going to have a nvideo geforce 6600gt
2 hard drives
1 floppy 1 zip drives
1 dvd burner
1 cd burner
More info dude, what speeds are all these drives going to be at? What CPU and motherboard? Also, output is only one factor to take into cosideration when buying a PSU, you need to figure out what rails you need, and what current they need on 'em.
Get atleast a 400w like neosteve said,just make sure you get a half decent 1 with a good +12v rail,you will want atleast an 18amp rail,and make sure it has enough connector's for everything you need to run.