Apples burn DVD-R and most Sony computers are DVD+R.  This could be your problem.  However, more likely is that you burned a secession rather than a disc.  Burning a secession allows data to be added at a later date to the blank portion of the disc.  Burning a disc, finishes the disc and it can not be added to later.  Most PC's can't read a DVD or CD that has been burned as a secession.

I shot a commercial job this week and stored a load of images on DVD for the client. I burned them all on my Apple G4 Powerbook using the Apple burning software OS X 10.2.8 and it all looked great. I delivered the work to the client who had a Sony Laptop, Windows XP with a DVD reader in it and although the disc mounted, none of the images showed up. I thought my Apple burned in a cross platform format. Any ideas? My only other choice is to give the client 11 GIG's worth of CD's (which she can read).

I have a toshiba laptop running XP that has a built in 1x DVD-R burner. I added an external USB2 4x DVD+R. I found that if I keep the amount of data UNDER 4 gig and finalize the disks, that I can read either on both drives.

May be something similar between you and your customer

Dan