POLKADOT  Forgot to mention it in my last post: of course you should replace the old Drive Genius application with the 2.1.1 update prior to burning the DVD. To do so you have to mount the converted dmg. Unmount it after replacing the app and burn the unmounted .dmg, not the mounted virtual drive.  
(Version 2.1.1)

POLKADOT  In reply to SJHA:

There's a menu command in Disk Uitility (under "Images") and a default toolbar icon as well by which you can select a .dmg to convert. Make sure to select "read/write" as the format for the converted image in the save dialog that pops up and do not encript the converted image. When the conversion is completed you can select the converted .dmg in the sidebar of Disk Utilily and hit the "burn" command, via the Images menu or by the toolbar button.

Be aware that the converted .dmg is much bigger than the original one (about 1.5 GB), but there's no problem to burn a DVD from it. BTW, I did all this running 10.5.6 and I'm not sure if it's working with Tiger too.  
(Version 2.1.1)

POLKADOT  This applies to owners of Drive Genius 2.1 who received a dmg to burn a bootable DVD with their version already.

You can simply convert that dmg with disk utility into a read/write one, mount it, trash the old Drive Genius.app and replace it with the the new one (v2.1.1). If you burn a DVD from this disk image you can boot your mac with it and use the new version without paying the 5$ download fee for an updated dmg.

The updated "old" DVD still has MacOS 10.5.5 on it of course, butl it works flawlessly with my (early 2008) Mac Pro.  
(Version 2.1.1)