Flash CS3 crashing all the time

Hi.
I am a flash games developer, and I am currently working on a game that is truly massive.
The main file size is over 250MB.
It’s been a work in progress for about 4 months of solid work.
Due to the size of the file, I prefer to create things like characters and objects in another file. I then need to import it over, replacing old movieclips.

When copying and pasting now, it always crashes, or tells me that its run out of virtual memory.
It appears to be impossible to get it all over, even bit by bit.
I’ve saved and compacted, I’ve saved as, I’ve moved it onto another disk drive.
All of the above seemed to help temporarily, but I’m now at a stage where nothing is working.
I don’t think the file is corrupted in anyway. I’ve had no problems with any other component of flash. Just the copying.
I just don’t understand what’s so intensive about moving over an object of about 10-20 mb.
My computer is quite high performance, 5.6ghz, 4gb of ram.

I’ve asked for help on so many forums now, and all i get is criticism at my file size. Well it can’t be helped. It’s a massive game.
I’ve tried using a runtime shared library, but unfortunately it doesn’t allow attachmovie to get it from the library. It seems the identifier is only being used to connect the 2 libraries when you set up a runtime shared library.
attachmovie is very important to the code and it can’t be done any other way.

Please please help.
I’m at a point where I need those movieclips in the main file…