Bring up the page in your browser. Then click on the VIEW menu and then click on the SOURCE menu item.
What kind of HTML field is ASP.NET producing for that text box??
Unless I am much mistaken, it will be a <TEXTAREA>. And, yes, an HTML textarea ignores embedded HTML and just displays it as text.
What you could do is simply replace the HTML <br> tag with a vbNewLine character. But that won't solve all the other possible HTML tags: <b>, <p>, [u], and more.
You probably need to use one or more REGULAR EXPRESSIONS to do the replacements completely.
But here's a question: Do you NEED to allow the user to EDIT this data??? If not, simply do *NOT* put it into a textbox! Just put it into a LABEL, instead. Voila, it should work.