That sounds like the problems I was having with some of the streaming programs.
Here is my solution to streaming to the XBOX... TRY THEM ALL! Find one that works, and stick with it. Each one has pros and cons. I recommend trying them in this order:
1) RElax (XNS): Great program with virtual folders (Ie: you can share several directories through one virual directory)
Con: Buggy like none other for me. Up and running fine one minute, and then the next it can't find anything and locks. Resetting the PC reaks hacok on the network.
2) SMB (Samba): Very easy set up. Just share the files on your PC, and tell the XML of XBMP where to look for them. Does not require any third party software.
Cons: Because the XBOX is in essence "sharing" the file in a concrete way, you are not allowed to play any files over 2 gigz (the FatX limit). Other than that, works great for me.
3) BXStream (XNS): Small program that worked great for me, although it is only in its infancy right now. However, with upgrade to XBMP CVS 2.4, it locks up when scrolling through the files.
Cons: You can not specify which directory to go to. Each time, it shows you all of the drives on your PC, and you have to navigate to the right directory (which could be very useful if it would remember the last DIR you were on). Also, you have to install M$.Net for this to work.
4) CXstream: This uses the third protocol. I tried it, with limited success. It seamed to stream well, but larger files literally took forever to start playing.