DVD write problems on my MBPro

[slim tim slide]

I've been generally delighted with the 15" MacBook Pro I bought from the refurb store about 6 weeks ago - in fact its so great it's scary BUT - having downloaded some much wanted movies i'm encountering big problems burning them to dvd through finder. one movie is in mpeg, and seems to burn fine to a dual layer tdk dvd+r (which i assume is a decent brand!) and plays fine straight from the files but when i put it into my normal dvd player it pauses at random intervals (not always in the same places). i know the player is ok and ive now used 3 dvds using the 3 burn speeds offered by finder - same problems every time.

second prob is that the other movie is in avi format and i cant seem to convert it - i downloaded prism converter but it says it cant find the source files thought they are in plain sight on my desktop and play fine through vlc, but i cant burn it to dvd!

Any suggestions very welcome - i dont want to be limited to watching solely on the mac!