I use cheap computer fair DVD's so i wouldnt think its a disk issue, i have two internal dvd writers and can write to either. i use Ulead DVD Movie factory to create my movies. and Nero Burning Ultra Edition V22.214.171.124 for copying discs. copies are ok and playable in any dvd player i have got.
my initial thought is with the USB connection, if you are using a USB hub, it might not have enough power (or maybe you have a lot of other things connected via USB)
If the USB upgrade is via a PCI-USB 2.0 card then you should be ok with the power bit.
usb hubs are notoriously bad when connecting items that draw the power from the pc instead of their own power source ie speakers or USB mice/keyboard etc.... if you have lots of USB items attached, unplug what you can and try again
ps. i use Logik CD/RW and Traxdata DVD/RW to test out a burn before doing for real so if it goes wrong then i can just erase the disc and try again. might be worth a try.
one last point, have a look at DVD shrink, its free and will copy DVD's quicker and easier than Nero, it also shrinks a Bought DVD down to a size that will fit on a normal 4.3gig dvd disc.