OK, I would use a client side script to do the search and highlight because a postback to the server is unnecessary. You already have the data on the screen in front of you and highlighting text is a view based operation.
So, using something like jquery is perfect. You would need the input box to accept the user's search term and, on the button click, run the script.
If you don't know jquery there are plenty of tutorials online and it is a very good tool to learn - you can have a lot of fun with it.
Once you've played with jquery a bit and learnt the basics the link I provided has all the information you need to incorporate it.
But, if you try and have trouble, post up how far you get and we'll help you out.