Hi,
psu : seems enough. Though, the global 450 watts of your actually are divided into several tensions (volts). So maybe your psu gives about 50W in 3.3V, and 250 in 12V, plus 150 in other tensions. Each family of connected devices uses a specific voltage. Cpu's use 3.3V. That's what edfair means by 12+ : 12V is the voltage used by your disks.
About hd + dvd on the same card, no problem. Usually, pci controller cards give you 2 more ide slots (ide-2 and ide-3), so you can connect up to 4 new devices (2 slots x 2 drives per cable). I think you'll have no problem even connecting both your new drives on the same ide slot (cable). Just pay attention to use a 80 pin parrallel cable for the 3rd hd.
Cheers,
Grunt