Installing OS X - no destination disk

I'm putting OS X 10.4 on an old G3 iMac. I've upgraded the OS 9.1, updated the firware and booted from the DVD. I choose a language and then I get the 'Select a Destination' screen. Below is blank though - there's no hard drive on which to put the OS on.

I can't find anything on Apple's site about this.

The G3 should be good to go, with plenty of RAM, ethernet and DVD drive.

Update - I found this: http://docs.info.apple.com/article.html?artnum=106235
I don't really know what it's on about, but if the hard drive isn't suitable, can i install to an external Firewire HD and use that for everything?

Fixed it! I had to reformat the HD into HFS+ with Disk Utility.

I always seem to post problems on forums and then figure out the answer 10 minutes later!

Next time, stop, take a few deep breaths, walk away, if necessary, get a cold drink of water, then go back to the problem. It solves most issues on the spot.