I am new to Inquisit, but I have just set up my script and ready to send a url to participants.

However, whenever a participant goes to the URL which I have provided them: 

Launch Page: http://research.millisecond.com/sarahlee/REAL.web

They apparently have a lot of trouble having to downloading Inquisit (which comes up as 'unsafe') and then Java, and after all that the IAT will never actually load..

Am I giving them the wrong URL? What's going on?

I was under the impression that having a web licence would make it easy for participants to undertake an IAT.  

To participate in a web experiment, the Inquisit "engine" must be delivered to the client machines somehow. Various delivery methods (JavaWebStart, Firefox / Chrome plugin, ActiveX, ClickOnce) exist to accomodate for different operating systems and browsers.

You can find more details discussed at e.g. https://millisecond.com/forums/Topic10005.aspx#10005.

Hope this clarifies.