ereg() violence

I have been screwing with this thing for 7 hours and CANNOT get it to work. When the author submits an html message the script needs to: replace tags like <br>, <p>, <div> with \n replace HTML codes with text equivelent like &amp; with & strip all other HTML tags that have no place in a text message like <b>, <font>, etc. and it would be nice if it would find the img tags and replace them with something like <<http://www.isp.com/images/pic.jpg>> But I am running into some serious problems!! Either I can't get the regular expression right or it times out (possibly because the regular expression is wrong) I just don't know what to do. I think it would increase performance IF I could somehow code it to replace only what is there instead of searching for a every possible code whether it is there or not. Suggestions on this would be GREATLY appreciated Jess