Originally Posted by jticeman500
Or will all of these 32bit applications be force to share the first 4 GB of memory on the system?
Vista x64 will allow up to full 4GB memory window to any 32bit app. Tested :-) In fact, Vista x64 is the best OS to run 32bit apps, as no 32bit OS can offer full 4GB of address space to application (don't even think about PAE).
Anyway, both programs you mention - Photoshop CS4 and LightRoom 2 are native 64bit apps on Vista x64 (unlike on obsolete OS X Leopard), so you won't be even limited by 4GB "32bit limit".
I am thinking about moving from 8GB to 16GB (P45 chipset can handle that), as having SQL Server 2008 Standard, IIS7, ASP.NET running in the background, and Photoshop CS4, Outlook, etc. in the foreground, can utilize 8GB RAM easily.