Hi!The horses are beautiful! You've got a great site going. I especially like the barn cam.
The others have hit on the things that most need changing.
First, those hover buttons: The reason they cause so much problem is that they are Java applets. They require a lot of RAM to load and some of us just can't handle it, especially if we have a couple of browsers open, maybe another program, etc. Yes, my browser crashed.
And I was using NN this time, but it has also happened to me in IE.
Frames have problems, too. Let me just refer you to this article so you can see the pitfalls and also check whether or not you have used them correctly: http://www.useit.com/alertbox/9612.html
I think your header would look better if it was a little smaller and maybe a drop shadow applied to give it a little depth.
Ditto the earlier comment on the backgrounds. They are distracting and make the text hard to read.
You have lots of good content! 
Best wishes,
Sandy
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www.alleghenyweb.com