Have a look here
Seagate How to guide it explains most things.
I pesonally have used Seagate for 10 years or so and, so far have not had a major problem, I did use their Tech support once, they were quick and good.
As for the ATA 100/133 thing, I think if you put a 133 drive on a 100 connector it will work but only at 100.
Seagate use diskwizard installation software which is easy to use and simplifies things for you.