Didn't read the page, but the bits I glossed over reflect my recollections:

http://www.macgeekery.com/tips/cli/nondestructively_resizing_volumes

I don't know if you need an Intel Mac for this to work. You may have to boot from another drive (e.g. external hard drive, CD) in order for this to work.

The other option is to upgrade to System 6 and use the Apple HD SC utility.