I have a solution with just under 100 projects in it, a mix of C++ and C# (mostly C#). When working in VS2005, the working set of Visual Studio is considerably smaller than
You can try using the Solution Load Manager. It'll let you mark some of the projects files as load on demand or not load at all. That may help.
If you're on XP, upgrading to Vista or Windows 7 will help as it uses WPF. May reduce the memory footprint of the UI rendering which would otherwise have to use compatibility mode.
A 64-bit OS should help you out a bit here, if you get more than 4GB of physical RAM. A 64-bit OS can provide 32-bit processes with a full 4 GB of virtual memory, whereas a 32-bit OS only can provide 2 or 3 gigs at best, depending on how you boot the OS.
That being said, 100 projects is a pretty fat solution file. Maybe now would be a good time to reexamine that decision...
EDIT: Running dumpbin /headers as prescribed in the article for DEVENV.EXE returns:
File Type: EXECUTABLE IMAGE
FILE HEADER VALUES
14C machine (x86)
4 number of sections
4BA1FAB3 time date stamp Thu Mar 18 06:04:35 2010
0 file pointer to symbol table
0 number of symbols
E0 size of optional header
122 characteristics
Executable
Application can handle large (>2GB) addresses
32 bit word machine
So that would indicate that an x64 box with > 4GB of RAM will probably improve your experience. You should have up to twice as much VM available for Visual Studio under a 64-bit OS...
The best thing you can do is to split up your solution. Visual Studio wasn't meant to handle so many projects in the same solution and does suffer performance problems as a result. Splitting up your solution into 5 different ones will make things better.