tautitan, If the video plays ok on your PC but lags on your player then it maybe that the video is encoded to high for your player to handle.
Be sure that you have a decent codec pack installed like K-Lite Mega Codec Pack.
Try lowering the audio bitrate settings and see if the problem improves.
What resolution are you encoding to 320x240?
Did the player come with a sample video if so could you upload it to
www.uploaded.to and leave a link for download so I can see what settings it uses.