Load Testing and performance

We have an asp application some of which will be being ported over to
asp.net so this may be a little OT. It is having some bad performance
problems and we need to isolate which areas are causing the problems. The
main performance problems are database related i.e. timeouts and deadlocks

Some questions:
Microsoft's ACT. How is it better than the Web Stress Application Tool?
Is ACT purely .net or can be used to look at any web app.
What is a good way of assessing which pages are causing the problems.
How can I relate the performance of the database to the application. The
system has LOTS (this app has 1000's of pages) of sql passed as strings will
this affect how easy the profiler is to read.
I suspect there are lots of memory leaks, are there any tools to look at
what is being left in the memory.

I guess what I want is a tool which will identify which pages are hogging
the most resources and if they are not being released so we can look at
optimising the code.