A few things to note:
First, make sure it's not just an issue of not enough bandwidth for the movie to play. Make sure you have a great reception to your wifi router and test with it almost side by side if possible.
If that can be eliminated as an issue, the next thing to consider is the format of the content you are trying to play. Various media servers and/or platforms will play different content better than others. I believe that Medialink used to have a problem, for example, with DivX and certain audio formats. The result would be a video that plays just fine . . . except for non-stop stuttering (plays for two seconds, stutters for one or two, endlessly). However, on Playback, it worked just fine.
Next, I would personally advise a very full featured program that works on XBOX 360 and PS3 and other devices called
Playback I gladly replaced the Nullsoft product with it and have been using it for awhile, now ($15).
Finally, I would be concerned with the format you are playing. It needs to be supported by the client (note that Playback is working on transcoding features, but there are some licensing issues they're bumping up against). See the lists of supported formats for the consoles, below:
Playstation 3 XBOX 360 If you have other formats that you want to play and are having trouble with them, I'd advise using something like Handbrake to convert your files to another format (which can, granted, be a hassle in many cases).