If I buy a server on which I\'ll be able to put as much RAM as I want, how much RAM can I make available for my asp.net web app using the latest versions of everything?
Increasing the memory to 6 GB or more on the server won't help because 4 GB is the maximum for addressable memory for Win-32. You would have to go to Win 64 in order to add more memory to the server configuration.
If its a dedicated is box, you can try running with the 3GB switch, which would allow the asp.net to use up to 3GB.
You should also check what your current max memory is set to...!?