The easiest thing to try might be increasing the buffer size on your media player and/or trying other ones such as core player.
You may want to try messing with some of the TPC/IP stack settings such as increasing the receive window size to larger multiples of 1024.
MTU is also an important setting, but must be determined by pinging the remote machine with different size packets until you find the largest one that doesn't time out.
http://msdn.microsoft.com/en-us/library/aa924893.aspx
and the link it has to IPv4 registry settings is a good place to start. Just change settings for the wifi adapter when possible, not global settings.
Another work around would be to convert the movie files to a lower resolution.
Wifi b and g aren't designed for speed. They're designed for getting a signal at longer distances from the wifi hot spot. Wifi a and n are the fast ones, but a has the shortest signal reach.