NEC 3500 or 3520 reading advice

I recently upgraded from a slower Sony DRU-530 burner to an NEC 3520 (firmware 1.4) to go along with my NEC 3500 (firmware 2.19) and found that both have problems recognizing certain DVDs that the Sony was able to read with no problems. Is there something I can do to improve the reading performance on either drive?

My system specs are:
1.8 Ghz P4
512mb RAM running XP home ed w/service pack 2

I think that many or all of us with NEC 3500 drives (maybe 3520 also) have the same problem. The only thing that I came up with was buy a second drive (that will read better.) I have a cheap BTC 1016. Maybe someone else will have a better answer.