When you type a command in the shell, without specifying the exact path the shell looks at an environment variable called PATH which contains a semi-colon delimited list of places to look for programs. If it can't find the command in these places it returns the "Command not found" message.
Make sure either a) the path to ndiswrapper is in your PATH environment variable, or, b) (my preference) that ndiswrapper, or a symlink to it is in /usr/bin, /usr/local/bin or any other path that's already in your PATH environment variable.
You can view your environment variables by typing
set at the shell.
You can find the location of installed programs on your linux system by using the
whereis,
find and
slocate commands in the shell.
Hence:
$ whereis ndiswrapper
Should return a path to ndiswrapper.
I found these with a quick google search:
Basic Commands
Whereis
Finding Files
Just out of curiousity, why didn't you configure the source before running make && make install?