I got a big assembly in Inventor R10.
It is very slow to work with and Inventor closes down now and then. There is also some segment errors.
All subassemblies are demoted to derived components.
 
How can I make it easyer to work with???

What is the number of assembly components? How much RAM do you have and how much memory is consumed by Inventor (see Windows Task Manager)?

There is only 2 different assemblies and 42 different parts. But I guess that about 20 of the parts is derived components with broken link.
I got 2000 MB RAM. Inventor is using about 1200 MB RAM. 

It is not that bad and big. Have you the Inventor 10 Service Pack 3a installed? Any adaptive components?

Yes I have Autodesk Inventor SP3 installed. I got one part with adaptives in. It is a part with a lot of constraints too.

Goto the Autodesk website and check you have the correct graphics card to run this software.

Graphics card is very important, i have try assamble over 4000~ parts. suggest wilcat vp880 pro or heigher ... firegl v7200 up... more beter