Thanks you 2!
Mad dog, it also states that I cant use a external hard drive for it?
mmm

Its going over my head a little as it does say yeah about erasing?
I guess im just extra cautious about doing it.
Im gonna check it out...
and I get back to you if thats o.k...
If DU says it can't use your external drive for the clone, it might be because of the ext. drives format. Most drives will ship either NTFS (Windows format, Macs can read files, but can't write files) or FAT ("MS DOS" format which both Macs and Windows can read/write). Some ext. drives are Mac specific in which they will be HFS+ formatted out of the box, but that isn't common unless you purchased one from the Apple Store.
In DU, if you select the external volume name on the left hand side, at the bottom of DU it will tell you its format. If you see MS-DOS, FAT, or MBR (Master Boot Record) anywhere, than it'll have to be formatted for mac (if you've used the drive in the past to copy files then it's not NTFS).
If you want to format it (erasing anything on it) select the drive in DU and then switch to the PARTITION tab, select the Partition pull-down menu that says "CURRENT" to "1 Partition", then click the OPTIONS button below and select the appropriate partition scheme (Apple Partition for PPC), and then to the right there is another pull-down menu for "Mac OS Extended - Journaled".
Give it a name and then click APPLY and it should be good to go after it completes.
Also, if you are using USB 1 (your PB G4 may be 2.0, can't remember off the top of my head) it will take a very very very long time for the clone to complete, probably an overnight deal. If it's USB 2.0 or FW than it will be far quicker but could still take an hour or two depending on the amount of data.