A couple things can cause problems with burned DVDs:
Do not burn the disk "overnight" while OSX maintenance routines might be running automatically.
Try running all routines manually, then restart the system prior to initiating the burn. ("Onyx" is a freeware utility that greatly simplifies running these routines)
Be sure you have enough disk space and adequate transfer rate for the files. It's amazing how quickly a 60GB or even 80GB HD can fill up when working with DV.
You need lots of free space for this type of work.
Two HD are definitely better than one with regard media authoring, and the faster/bigger the drives, the better.
An external Firewire drive might actually perform better than the internal drive in your Mac. (Check Macgurs.com forums for recommendations; those guys are very knowledgable in high-performance storage solutions)
Moving the "Users" directory to another drive and controller can significantly reduce the load on your system drive, allowing it to perform better during demanding tasks.
(Macgurus.com for detailed instructions on moving the Users/Home folder correctly)
Try restarting the Mac prior to burning your disk.
Use lower speed media; Lower burn speeds are often much more reliable.
The burn time will be impacted, but the asset encoding is likely to be the most time-consuming process anyway.
Use high quality media($); it's often less expensive in the long run, unless you actually need lots of coasters. ;P
Converse to your experience, I recently had a problem playing back a DVD authored using WinXP; only one player in five I tried would even recognise the disk.
(neither of my Macs could read it, nor could my $600 Marantz set top player; very frustrating)
I've experienced minor problems with some DVDs I've burned on my Mac, but never to this degree.
Apple tends to put a happy face on this technology, so the failures are all the more frustrating, but rest assured that you are not alone.
Truth be told, the laws of physics are not repealed when you buy an iMac or Mac-mini with DVD authoring tools included. (Powermac with at least two very fast high-capacity drives and lots of RAM is the ticket for "trouble-free" multimedia authoring)
GL