I'm having problems with Flash under ubuntu and was going to try and upgrade to the Alpha release of Flash 10.1.
The problem is that it came as a .so file, and I can't find any information as to what this is.
An .so file is a compiled library file. It stands for "Shared Object" and is analogous to a Windows DLL.
Often, package files will place these under /lib or /usr/lib or some place similar when they're installed. If you extract an .so file to a location in your $LD_LIBRARY_PATH, a program that requires the library should be able to use it.
Ideally, read the accompanying documentation to ensure that it's in the right location.
If you run a command like
It is a dynamically linked shared object library, analogous to a .dll file in Windows.
Here are a couple of posts for installing Flash 10 in Ubuntu x64 and x86:
Make sure you've uninstalled any previous versions of Flash befor installing 10.