There are several ways of doing this - ever read Javascript for dummies?
There is one script in that book (I hope it was in that book...) that is of particular interest for these situations and can be easily rewritten for sending the output of that script directly to your inbox even without the person on the other side knowing it. One click at the URL address you posted to someone and it returns so much information about the user's system and... Ta-Da, IP address that you can start tracing it in no time by either whois.net or the url Redleg posted...
PM if needed.