Power Mac G4--Replacing Hard Drive

Hello,
I have a 2000 Power Mac G4 model #M5183. I've been using (prepare to laugh) FCP2 (go ahead and laugh!). I overloaded the secondary drive (for media only) and now I want to replace this drive instead deleting the footage on it. So I went to my local Best Buy and after talking to a salesman, I bought a Western Digital SATA 300MB/s, 500GB/Go, WD Caviar SE16, 16MB Cache, running at 7200RPM. Okay, I have no idea what most of this means.

Is there a possibility that by installing this drive I might screw up the FCP or the OS--it's OS9.
Is there a way to install the new drive and keep the old one in it? Or am I better off taking it out?
Of the two drives already in it, which is the main drive, which is the secondary?
The one drive I can see has an IBM label on it.
Once the new drive is in, will I have to format it or will it be automatically done?
Or should I just pay someone $50 to put it in?
Thank you for the help.
Daniel

Power Mac G4s can't take SATA drives. You need an IDE drive for that model.

If you can't return the SATA drive, just buy a Firewire 400 SATA enclosure and put the new drive into it.