DVD burner problems

We've tried 4 different DVD burners, 3 internal, 1 external, and have the same problem. You can load files and burn 1 DVD, but after that is done and you try to do another one from different files, it will not 'unload' the first one. You have to reboot the system to create another DVD. We have installed the latest BIOS for the motherboard, but it did not solve the problem.

Computer specs: Windows XP, Intel D975XBX2 motherboard, Intel Core 2 Extreme X6800 processor, 2 GB Ram

(The DVD burner in the 'Product' list is not necessarily the one we've used, but I had to pick one to submit my question.)

Any suggestions?