question about page extensions

I have a question. I just finished re-building a site for a local non profit agency for abused kids and have run into a problem with exterior links. They had their old site build using Frontpage using .htm extensions on all their pages. I didn't know that when I built the site, so I used .html. There are a bunch of exterior sites that link to different pages of the old site. I was thinking about building some redirect pages in the file structure as the linked sites are found. My question is, can I have .htm and .html files in the site directory? I thought I read somewhere that they have to be the same.

For example here is one link from another site pointing to the old site pages:
history.htm
This is the address for this page is:
history.html

So I was planning on building a page with the same file structure of history/history.htm and adding a little redirect text with hyperlink ,and add this code above the head tag

<META HTTP-EQUIV="REFRESH"
CONTENT="1; URL=http://www.adriel.org/history.html">

Should this work?