Pro Tools Plug In Problems

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So I bought a new MacBook pro a couple months back and a new MBox Pro. When I bought it I forgot to register it and didn't upgrade or even use the Pro Tools program til I upgraded to 7.4.2. Now that I have Pro Tools up and running I am trying to use Amplitube 2 as a plug in inside Pro Tools. Every time I start it up it gives out after a bit. First thing that happens is that the comp will run sluggish. Eventually a message will pop up saying I am running out of CPU power and then audio will drop out. Other times no message will appear and it will just drop out unexpectedly. I have the Hardware playback settings at Default mostly because I think my CPU should be able to handle them no problem on such a basic setup.

A couple things to note:

1. I am running plug ins wrapped as VSTs. (I tried the other way with the same results)
2. When I use Amplitube 2 as a stand alone it works flawlessly.
3. When I run Amplitube 2 I make sure I don't clip in the program.
4. I have the same results when I run Addictive drums (it just takes longer for audio to drop out)

So my only common sense guess would be that it's not the plug-ins or Pro Tools itself but something with the computer.

Is anybody having the same problems?
Will I benefit from just re-installing my OS and starting fresh?
I've tried optimizing my system but am a little unfamiliar with Mac Os's and what should be running and what I could do without under the Activity Monitor Window.

Also note that I downloaded a program called IFree that is supposed to optimize the RAM space on your computer when run. (The problem started before).

Sorry for the long winded letter but I thought it would help to be as specific as I can. I've posted various topics in other forums and so far no solution. If I don't get this fixed I'm going to have to resort to solely writing acoustic songs!

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MacBook Pro 17"
2.4 Ghz Intel Core 2 Duo
4GB 667 MHz DDR2 SDRAM
Mac OS X Version 10.5.4

MBox Pro
My Book External FireWire Drive

Pro Tools LE 7.4.2
Amplitube 2
Addictive Drums