Messenger Question!

Not exactly a DB question but the storing will be done in a DB and using PHP. Anyways with the growing demand of IM's I want to add to my site easy access for people contact me. I could add my Yahoo! username for Yahoo! Messenger and MSN Messenger email address but I want to make it easier for people to add me, most people won't bother doing it the long way. So want I want to do is store my id's to a DB than run a query to fetch the id required than output a hyperlink to the user to add me. When they click the hyperlink it will automatically detect if they have got that Messenger system on their system and if logged in I will be added to the list. If not logged in or have the Messenger than it will display a error. Is there a way to DETECT if they have Yahoo! or MSN Messengter installed? Also I know the hyperlink code to add users from a url for Yahoo! Messenger but does anyone know it or some code for MSN Messenger? Thanks for your time. J