Hi Womble
I've never used Nero but the same kind of thing happens when converting videos to play on an iPod. Maybe the 2 movies you downloaded last night are in a different format to those you've burnt to DVD before? Might have to look at how you're converting them. For burning DVDs I use DVD Santa - it's really easy to use. Comes in a trial version (free) if you feel like checking it out (the trial version will add some crap to the top of the screen)
http://www.dvdsanta.com/

As for your Nero problem, check out the support site.
http://ww2.nero.com/nero6/enu/Nero_B...port_prev.html

There's an FAQ section & further support if you need it