My CDRW/dvd RW won't play DVDs. It handles CDs fine, but DVD playing doesn't work. Checking the logs I found the message:

Jun 11 22:58:23 kepler kernel: ATAPI device hdb:
Jun 11 22:58:23 kepler kernel: Error: Illegal request — (Sense key=0x05)
Jun 11 22:58:23 kepler kernel: Media region code is mismatched to logical unit — (asc=0x6f, ascq=0x04)

I dug around but couldn't find exactly what this meant. So I dug around for this message, displayed by mplayer:

libdvdread: Invalid title IFO (VTS_01_0.IFO).
Cannot open the IFO file for DVD title 1

After some googling I came up with a link to regionset, which can help me reset the DVD device to be able to play US DVDs. Regionset is available from the dag repository (which is disabled by default in FC3 but as configured – you just need to enable it in /etc/yum.repos.d/) and was very simple to run. For users of the aspire 1690 in the US, set the region code to 1. Users in other countries should check the regionset web site for which region to configure your drive for.

After running regionset, the drive works fine with US DVDs and mplayer.