AliensAreFuzzy said:
Then would it be possible to use that disk image to burn from a PC with the right software, and if so, what would that software be?
It's definitely doable on the PC. The DVD you create isn't copy protected, so you can easily rip and make copies of it. As for what software to use, I don't know anymore, haven't used a PC, other than for gaming, in a few years.
As for doing it on the Mac, it's done in Disk Copy (in Panther Disk Copy has been integrated into Disk Utility, so check there). Here's the procedure, straight from Apple:
http://docs.info.apple.com/article.html?artnum=42724
Good luck!
EDIT: Oops, I mis-read your post... I'm leaving the above, it could be useful information for you anyway. As for the real response to your question:
You'll have to convert the .dmg file (I'm assuming it's a .dmg file) to something standard so that a PC can understand, and burn it. You can use a program such as Nero to do it. But the file is huge. How are you transferring the disk image to a PC? If you're thinking of cutting costs and getting the Combo Drive and doing your DVD burning on a PC, that's up to you... but I suggest that if you plan to burn DVDs with the Mac mini, definitely do get the Superdrive, it'll make your life much easier.