Mod_Rewrite Redirect help old urls to new urls.

[D-Block]

Hi, I have an old 4images(php gallery script) site which uses an OLD SEO MOD

The OLD SEO MOD enabled me to have these urls like this: http://mysite.com/4images/cat87.htm

 

I want to use A NEW SEO MOD but I want to have my OLD SEO urls redirect to the new URLs so that I don't get penalized by google.

 

So basically, how would I be able to do this...

 

OLD URL: http://mysite.com/4images/cat87.htm ---AUTO REDIRECT TO NEW URL:--->http://mysite.com/4images/cat-yellow-cars-87.html

(THE ID of the string being 87)

 

Can I do this via htaccess? can i do this via PHP?

 

If you can help me out in anyway, even some hints of what I should do, thanks.