How much of the available RAM will a 32bit installation of Cubase 7 on Windows 7 64bit with 8Gb RAM be able to access please? I am deliberately not installing Cubase 7 64bit yet as too many of my plugins are not yet 64bit and I don’t want to use bridging software.
32-bit processes are limited to 2 GB of RAM (see http://msdn.microsoft.com/en-us/library/aa366778(v=vs.85).aspx for details).
The only real advantage of your 8 GB and 64-bit system is that each of your 32-bit processes can have 2 GB. Though your 32-bit Cubase process share the same fate. So, in short, you will benefit from running Cubase 64-bit, even if you have a bridge-o-phobia. 
So does that mean the 32bit plugins will still work on Cubase 64bit without bridging but they will just be limited to 2Gb?
Yes and No, 32-bit plugins work in Cubase x64, but WITH bridging.
You asked how much RAM could the Cubase 32-bit version access in Windows 7 x64.
On W7 x64, by running the Cubase 32-bit version, you are limiting Cubase to only 2 GB of RAM, but if you instead use the 64-bit version of Cubase, it can use all the available memory. The 32-bit plugins are limited to their internal addressing capabilities no matter which of the Cubase platforms you run.
Ok thanks, I understand now.