Windows 7 32 bit 64 bit usage

I have a new laptop computer with 64 bit Windows 7 Home Premium installed. I need to be able to switch to 32 bit usage to support my Autocad software. I understand that Windows 7 Professional offers that capability. Does that mean that once Windows 7 Professional is installed that I may manually select either 32 or 64 bit operation?

No you cannot switch between the 2,
How do you know you r CAD software will not work on W7 64 bit, most 32 bit software works on W7 64 bit? Have you tried installing the CAD software and running it in XP compatibility mode. You do this by highlighting the exe file for the program and go the compatibility tab
What it means is you can install virtual machine known as VM Software. There are many out there MS has Virtual XP and it is free. when you run the virtual xp from MS you just load your programs on the XP machine like you would any other computer. There are some caveats though, with MS Virtual XP, The default for full screen resolution is 16 bit there is a regedit you can do on the XP Virtual machine that allows for 24 bit colour resolution

I initially tried loading the Autocad, and found it wouldn't work. I checked with the Autocad website and found out that my version of Autocad (Autocad 2000) will not work with a 64 bit operating system. I read somewhere that Windows 7 Professional had the capability to work either as 32 or 64 bit. It seemed like there was a selection built in to where you could load it as 64, but switch it to 32 when software required it.

No there is no such thing, what they were talking about is with Pro or Ultimate you can run XP as a virtual Machine(Computer) You install programs on the the virtual computer just like any other computer. If you have 64 bit Pro, or Ultimate just look up MS XP virtual machine
A virtual machine (VM) is a software implementation of a machine (i.e. a computer) that executes programs like a physical machine.
en.wikipedia.org/wiki/Virtual_computer
http://www.microsoft.com/windows/vir.../download.aspx

In addition to what Super Sarge said, Please don't confuse XP compatibility mode with XP mode.

XP Compatibility Mode simply changes how the applications are started and run.
XP Mode is Windows XP SP3 32-Bit operating system running virtually within Windows 7.

How do I tell if an application is 32 bit vs. 64 bit

Try using Virtual Windows XP mode.