Backing up entire drive (10.4.11) to FAT32 external for complete wipe
FAT32 isn't up to faithfully preserving Mac permissions, links and metadata. If you cannot repartition the drive as GUID/HFS+ it would be best to make a Disk Image on the FAT and back up to that image.

If your drive was 120G and had at least 10G free space you should be fine with settings like this to create the image. The sparse image is nice since it only fills as files are copied but it can expand to the size specified if needed.



Then you could then use Disk Utility to "restore" the data from Macintosh HD to the mounted image file. The HFS+ data would all be properly encoded and stored in one big file on the FAT drive. I don't know file size limitations on FAT anymore so that would be the one flaw in this plan if you needed an image larger than could be stored on the drive as formatted.