Just to make it 100% clear - all Gigabeat users need to update to the latest bootloader (available via the link in the install section of the manual) in order to use current Rockbox builds.
You should update both the bootloader and the .rockbox folder at the same time - i.e. connect your gigabeat to your computer, copy the new FWIMG01.DAT, extract a current rockbox.zip, unattach, then power-cycle your player with the battery switch.
If your Gigabeat freezes with the "Rockbox loaded" message, that means you have an old bootloader with the new Rockbox. You need to power-cycle your gigabeat, and hold MENU as it boots. This will put you into rescue mode and you can attach your Gigabeat via USB and copy the latest FWIMG01.DAT