VS 2008 Reading Webpage Source And Filtering String Data?

My program so far reads a certain webpage's source code and places it in a textbox. This much has already been accomplished.

Now I need to pick certain strings out of the rather large amount of text data and have the lines stored in variables, but the trick of it is, the exact string is unknown. The exact function should be, that the code finds certain tags from the source code, say <td> and </td> and takes the string data in between those tags, what ever it may be.