Blu-Ray Drive on PC weird stuttering

[robestyles]

Hey Everyone I just bought a blu-ray drive for my HTPC set up. The Sony BDU-X10S. Currently I only have 3 discs to check with it (Helloby, Yuma and the demo disc it came with). I have both PowerDVD and WinDVD but I am experiencing some weird stuttering problems with them. The weird part is that sometimes it stutters and sometimes it works perfect pending on the movie/software.

I have been doing some research and most solutions seemed to be with the CPU specs and/or driver issues. My problem though is weird in that it sometimes does work. At first I thought I just need to upgrade my PC but if sometimes it's working now I'm thinking my PC is more than capable and its a software problem. Everything is updated to the latest drivers/software. Here is what I currently get

With PowerDVD:
3:10 to Yuma Perfect no stuttering at all

Hellboy: At first it stutters but if I close Power DVD and then restart and choose resume were it left off it works perfect no stuttering. It I dont select resume and click start from begining it stutters again.

Sony Demo disc: This one is weird if I play it by itself it stutters really bad. If i close and restart it stutters bad BUT if i play Hellboy first then put in the demo disc and choose resume playback it works perfect.

With WinDVD:
3:10 Yuma works perfect

Hellboy/Demo Disc: Both stutter pretty bad no matter how I start them up.

My current specs are:
Athlon X2 64 4200+
Nvidia 7600GT
2MB Ram
WinXP

I was thinking about upgrading the graphics card (something cheap no gaming this is just purely for movies) but I'm not sure if that is going to fix my problem. Any suggestions?