Yep, linux is the best choice if you don't need ASP.
BTW, you can set 404.asp to do 301 redirect.
Read
this to know how to use 301 redirect.
Add all the redirects in 404.asp file and set it as default 404 error handling file.
Then delete all html pages that you have set redirects.
that's it.
Now if someone try to view the html file, server will call 404.asp file as there is no such .html file. Then 404.asp file will send 301 redirect to the browser.
HTH.