Doesn't matter dude, those SATA drives are power hungry
Beep beep beep. Bullshit detector going off!
Don't pull this crap on boards where there are actually clued in users, ok?
SATA drives do not consume significantly more power than PATA drives. The only difference between the two is the electronics, and they're a miniscule power draw in either case (they run off the 5V line). The motor is what is a large power draw in drives, it's what runs off the 12V line, and it's only a very large draw on spin up. The amount of power needed to keep the platters spinning is pretty small, comparatively.
Firingsquad still has the best PSU guide I've seen. The numbers they give for CPU draw are outdated now, but those can be found from the manufacturers easily enough. If you don't want to do all the math though, here's a simple rule of thumb -- if you have a 350W PSU with a +12V line under 12A, throw it out. It will not have enough juice to power a modern CPU, a HD, an optical drive, and a modern video card (even without the video card it's questionable).
Good 350W PSUs will have a +12V line at around 15A. Above about 18A and you're probably talking about a higher rated PSU. But you probably don't need bigger unless you're running a lot of drives.
Don't buy a bigger PSU than you need either... it's a waste of money. Do buy a quality PSU -- go with a name that's well known and trusted. The output power is more likely to actually match what they claim and is less likely to have tons of noise and other problems.