DVD drive plays half the movie before failing

I've searched all over the net and this site, but can't seem to find this problem anywhere.

My DVD-Rom will play CD's, Data DVD's and some DVD movies will play fine.
About half way thru the movie it will pause and seems to be trying to find the disc.
I can eject the disc and restart the movie from the same position, sometimes it will return to normal, othertimes the problem will continue.

If I try to play the movies in the DVD+RW, it will play for some time before pausing and "loading/copying data". The DVD and the HDD spin up.

This happens with dual and single layer discs.
I have cleaned the discs and the drives. I've also reinstalled the drives.
The discs do work a stand alone DVD player fine.

Thanks in advance to anyone that can help.

WinXP Pro SP2
Pent 3 866Mhz
512Mb Ram
Geforce FX 5200 (128Mb)
80Gig HDD (about 5Gig free right now, but the problem also happened with over 20Gig free)
DVD-Rom: Lite-On LTD-166S
DVD+RW: Ricoh MP5240A

DJ Manning