can't instal xcode 3.2.5 on my Snow Leopard

Hi everyone

I have a problem installing xcode 3.2.5 with ios sdk 4.2. I made sure the download is checked for consistency. THe image got mounted. double clicked on the package, licences accepted, password entered. start install, and a few seconds into install the operation is interrupted and an info appears: unknown installation error occured.

are there any steps that could be taken to diagnose and eliminate the problem ?