New HDD for iMAC G5 with isight

i have an imac g5 with isight on it, and i finally managed to swap out its dead HDD for a new WD 160GB SATA drive.

now it wont let me partition the HDD properly. i go to utilities, disk utilities, then try to partition it. it seems like it begins to partition it and the progress bar starts going at the bottom, until it gets maybe 25% across, then just suddenly completes. the new "partition" it creates has no available space, doenst have the name i specified, and wont verify because it has "an error" and will not repair because it has "an error"

does anyone have any idea what is going on?

note, i didnt partition the HDD before i installed it, which is why im trying to do it now.

Hi Davy
I can't just remember if you can perform a 'live' partition. Firstly you need to back up your drive to somewhere other than the hard drive you want to partition then put in your original OS disk and click "install Mac OS" it will then prompt you to restart. When it has rebooted you can access "Disk Utility' from the apple menu drop down menu. From there you should be able to partition you drive from there