Blu-ray stutters on BDC-202

I wondered if anyone had a similar problem as I do w/ my new Pioneer BDC-202 that stutters when playing blu-ray disks. DVDs play okay and this only happens w/ blu-ray disks. I am using an NVIDIA GeForce 9800 GT card. The computer configuration is a little old but before I change the entire system I wanted to find out what exactly was the problem. I am using an onboard SATA connector and I read somewhere that it doesn’t really work well with this graphics card. Does anybody know about this problem?

Computer configuration:
AMD Athlon XP 2800+ 1.6 GHz
1.25 GB of RAM
ASUS motherboard K8 A31G

Thank you !