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Intermittent problems are often a result of interference. Interference can be caused by other networks in the neighbourhood or from household electrical items.
You can download and install iStumbler (NetStumbler for windows users) to help you see which channels are used by neighbouring networks so that you can avoid them, but iStumbler will not see household items.
Refer to your router manual for instructions on changing your wifi channel or adjusting your multicast rate.
There are other types of problems that can affect networks, but this is by far the most common, hence worth mentioning first. Networks that have inherent issues can be seen to work differently with different versions of the same software. You might also try moving the Apple TV away from other electrical equipment.
The following article(s) may help you.
Thanks for the tips, but after reading other comments on the similar problems I decided to take the ATV back to the dealer along with the model and make of my router. (this seemed the best way as I am not very computer literate) Anyway the router was the problem so now I have the Apple airport hooked up and no more stalling, but after each movie or program watched I sill have to boot up Itunes to watch the next show, which is now a lot better than before