re:
And they don't exactly run side-by-side. IIS either runs 1.1 or 2.0
...you can decide which to use, and flip back and forth, but you can't use both at once.
They can't be used at the same time *by the same application*.
But they certainly can run side-by-side, if used by *different applications*.
If running IIS 5.0, set your 1.1 apps to run either
in Low, Medium or High isolation mode.
You cannot have 1.1 apps and 2.0 apps coexisting
in the same Low or Medium isolation mode.
You'll have to run your 2.0 apps in High isolation mode,
or in Medium isolation mode if no 1.1 apps run in that mode.
For IIS 6.0, it's a bit simpler.
If you're running in IIS 5.0 isolation mode, the above precautions will do.
If running in native IIS 6.0 mode (worker process isolation) , running all
1.1 apps in one or more Application Pools, and running all 2.0 apps in
*different* Application Pools than any 1.1 app is running in, will do.
You can have any number of Application Pools, if you have enough RAM.
Just make sure you don't mix 1.1 and 2.0 apps in the same Application Pool.
That will allow you to run 1.1 apps and 2.0 apps
side-by-side, simultaneously, in your servers.