try turning off power mizer of course the 6800 can play back dvd's its probably some software driver glitch dvd reader, disc type, problem.
if its yuor dvd you'll get moments ware it freezes and player system dosnt respond and drive makes spinning up and down noises generally, if its continually choppy but dosnt freeze that could be the drive but the drive would still make non standard actions and associated noises, also could be a driver issue maybe a mad power mizer on some drivers i had issue of power mizer though on mains. check task manager and other system tools to understand what the issue is.
when it skips is cpu being maxed out ram / disk cache shooting up ( check with task manager) if the drive seemed normal and task manager read as normal but it just skipped i'd say clean yuor disc. Does it happen with just 1 film or many or cirtain types of data dvd ?
My system came with a sony drive which just didnt want to read the disks properly ( actually it was perfect tell one day i fancied watching the first series of sg1 i have on dvd and skipped froze and wouldnt see some disks) and after going through everythin suggested above and more i got dell to replace it i didnt know that would fix it but i made them do it and it fixed it, i have had alot of experience with various CD's and DVd readers and its far too common for them to just not get on with cirtain brands of disk to the point ware they wont even see some still i see that as faulty piece of hardware.