How can you tell when dot net 1.X is no longer used by any program and
therefore can be removed (via control panel)?
Since DotNet programs can be XCopied into place, you can't ever be truely
sure.
You'd have to sweep every hard disk on the machine and potentially sweep
network drives too if security settings permitted the running of code from
this type of location.
Even then there are applications that wrap the MSIL inside native exes which
would prevent most detection mechenisms from finding that the program needed
..Net
If you're prepared to install a later version of the framework then I'd suggest
you should be ok to remove.
Most applications written for DotNet 1.0 and 1.1 will run correctly under
2.0, 3.0 and 3.5
but there are always exceptions
