Internal Hard Drive advice

Hello all and a Happy New year.

Because you were all excellently helpful last time, I'm back with a different question or two.
I have tried searching but don't get the answer I need.

I have a G4 466, 640mb RAM with a 30Gb hard drive. Runs OSX and is used mainly as a music recording, video editing, picture editing machine. (I'm a switcher and this thing rocks compared to my Dell).
I am looking to add an additional hard drive and have seen the following:

Seagate Barracuda 7200.7 120GB UDMA100.

The write up says PC, PC, PC.
Its the right size, spec say ATA - 100 (which I am led to believe is right), is the maximum size a G4 of my ilk can recognise.

Will this hard drive work?

If it won't can some provide me with a make and model of an hard drive that will work?

Also, when I get said hard drive and install it, How do I make that the drive that everything is written to automatically. So my 30gb is the application drive and the 128gb stores my music, videos, word files etc.

Small but significant point, bought the Mac second hand and don't have any of the original discs. Can't get them either.

Cheers all
Lloydie