Why_me - 8:07 pm on Feb 8, 2000 (gmt 0)

I'm about to change the page file extentions on my site from .html to .shtml ; the thing is i will need to redirect a call to .html to the .shtml file because of all the external and se links. The pages are cgi generates and I can't keep the old files because of a conflict with the new ones. So how should i go about doing this?
Thanks
John