You have not provided enough information to make an informed technical evaluation.
First thing; you have to determine is whether you have a faulty box or bad video.
Virgin rip a DVD and bluray (do not use a copy) to a USB hard drive and play both the video you are having issues with and the ripped titles directly on the WDTV LIVE SMP; do any of the movies stutter?
If yes, you may have a faulty box, try a few more virgin rip titles. If the stutter is consistent, I would contact the WD service centre or return the box where you purchased it for a replacement.
If the movies play smoothly, then your network is the culprit.
I don’t own a WDTV Live SMP; I can confirm that PS3 Media Server works without issues on the WDTV Live. You don’t mention what OS you are using; I assume Windows. Play a virgin rip movie through your computer using PS3 Media Server, open the task manager and observe the network resources. PS3 Media Server will stream a virgin rip DVD through a 100mbit wired network, without trancoding using around 20 to 30% network resources. The CPU resources are around the same. If the CPU resources are higher, consistent around 50%, check for any programs running in the background. If your network card is 1gbit around 1% network resources use. Depending on the bluray title you may have stuttering issues, try the PS3 Media Server transcoding.
What happens when you use the Windows native network instead of PS3 Media Server?
