Re: computer vs DVD player?

I'd go to the drive manufacturer's website and check for a firmware update - follow all of the update instructions.
But, as you're noticing an issue with playback of commercial DVDs, the drive may be failing and need to be replaced. Or maybe the lense is just dirty.

Memorex should be of suitable quality, but I'd move to DVD-R when you go for your next media purchase.

Almost forgot, when using a dedicated burning app, usually there is an option to "verify" the burn. Your burns may have errors. It takes a few minutes to run a verification on a DVD, but if you want your work to last forever it's a small effort.

Can you pull the programs off the DVDs and get them back on your hard drive - this can sometimes determine if the burn was bad?