How is DVD different than CD?

[john_gore at yahoo.com]

Since installing FC2, I cant mount or write DVD,
either + or - . CD's work fine on this drive, both
mounting and writing, but not DVD's. Any ideas? Are
modules different for DVD reading or did I need
something special compiled into the kernel? Seems like
it should just be iso9660 and udf file support 

Thanks, JohnG

Detail:

Error while mounting

mount -t udf,iso9660 /dev/dvd
/dev/dvd: Input/output error 
mount: /dev/dvd: can't read superblock. 

Ive tried different DVD's (data, not audio) and
different media brands. DVD-R comes back with the
error instantly, DVD+R takes longer

>From fstab:
/dev/cdrom /mnt/cdrom udf,iso9660
noauto,owner,kudzu,ro 0 0
/dev/dvd /mnt/dvd udf,iso9660 noauto,owner,kudzu,ro 0
0

/dev/dvd and /dev/cdrom are both linked to /dev/hdd
and I did try mounting /dev/hdd without using the
links
Not using scsi emulation as I was under RH9
Running FC2 2.6.5 on athlon, MSI DVD +/- 8x (updated
with most current firmware)