Creating a restricted user from Inno Setup
You can call the NetUserAdd() direct from (Unicode) Inno Setup or write a small wrapper DLL/program that does it for you.
Using the code above is probably best, but I like the command-line since it can go easily under the [run] section without needing to write a method and hook it all up, etc. It does have limitations though.
[Run]Filename: {sys}\net.exe Parameters: user UserName Pwd /add