Hi Shaun, try this out and see if it works:
waithidden cmd.exe /C echo {parameter "IP" & " Our-Server-01.any.domain.dcd"} >> "{pathname of system folder as string}\drivers\etc\hosts"
In actionscript I often find myself replacing or omitting curly braces for parameters and files as needed. Usually I use () instead but sometimes you can just leave them out since they’re already in a relevance block.