Streaming Movie from one iMac to another

I hope this is a quick issue.

I have had a Mac Mini for several years connected in our family room to a Sony TV. We use iTunes to watch movies and it works very well. I have a 2 terabit external drive (iomega) with Firewire, but at this point the Itunes library is on the Mac Mini's hard drive.

I have another mac (27 inch) which has a larger hard drive and a Thunderbolt 6 TV Raid (3 tb mirror). I curently have the itunes library on that mac located on my 256 gig SD drive (second hard drive is 2 TB disk).

I was planning on moving the itunes library to the RAID and running movies in the family room via home sharing.

So last night we tried to watch a movie stored on my SD drive accross the wired network to the family room. It played fine for about 5 minutes and then just stopped. When I tried to restart the movie the Mac Mini said I could not because home sharing was not on! I checked it was.

I then used the finder to log onto that mac again and the movie showed up in the shared section on iTunes but again would not play for more than a few minutes.

So what am I doing wrong?

I was considering getting an Apple TV for the bedroom, but if I cannot successfully stream a movied from one mac to another on the WIRED network, what chance will I have with a WIFI connected Apply TV??

Mike