DVD burned on mac does not play on PC

It's a common problem. Not all DVD drives will read all recordable DVD's made on another drive. You might have better luck with a different brand of media or writing at a slower speed.

Virtually every manufacturer includes a disclaimer that their drive may not read all burnt DVD's.

DVDs created with DVD Studio Pro tend not to work well on PC, try finalizing the project, exporting to a third party program, then burning it.

Message was edited by: Peter Miller

I've had the problem Direwolf mentions. Recordable disks are hit and miss on what they'll play on. Read-only disks have the better chance. Are you burning to read-only disks?
Too, from this topic, http://discussions.apple.com/thread.jspa?threadID=2226083&tstart=0
you'll find a knowledgeable commentator who says this:

It is common knowledge, that Apple ROM in Apple shipped optical drives is crippled as compared to a similar version of the 3rd party manufacturers ROM.
This invariably leads to media support issues, speed issues, etc.
The web is full of people with gripes about Apple OEM optical drives.

The firmware issue also runs the other direction.

Many PC users do not keep firmware up to date, which creates compatibility problems.
Most firmware updates are for media compatibility. If a drive uses old firmware, then it does not have firmware support for the latest media.

Other factors:
http://support.apple.com/kb/HT2882?viewlocale=en_US

Media also changes by maker and batch, so bulk, no name and economy brands should be avoided at all costs.
http://www.digitalfaq.com/media/dvdmedia.htm

Burning DVD for Mac/PC should be done in the HFS+/ISO 9660 Hybrid format, or one can expect problems across platforms.

Burning too fast can also create a disc that is unreliable/unreadable.

In OS X, burning through Disk Utility can provide a more robust burn as compared to other software.