Powerbook, and Mac Mini together?

Do you want a desktop is the main question.

That sounds like you want to use the Powerbook display with the mini. That won't work. The powerbook DVI is DVI out, not in. You could use a VNC client though like this one.

buy and external drive

VNC is slooooooooooooooow and as we have just learnt, iDVD 5 will let you export a disk image so now you can use an external drive. Go get yourself a Firewire or USB 2.0 DVD burner if thats all you need...

i already own a dvd burner on my PC... so when i bought my 15" pb 8 months ago i opted to not get the overly expensive superdrive. i then bought an enclosure for my dvd burner and since the dvd burner isn't even a main drive in any computer i simply plug and unplug as needed to whatever computer would need the burning capabilities.. much better than spending $150 or whatever it was for a superdrive... instead i spent $60 on a 8x dual format burner, and $30 on an enclosure and now i have the ability to use it on any computer i need in my house.. more useful than having a superdrive in my powerbook.. i don't usual burn things on the go though.