'Join' fields - URL linkable.

I want to create a drop down menu in the join form where the user can select an option with a URL associated and then have a pop-up window open to that url .  Is this possible?

Thanks

Nigel

Yes if you make system field and make function for this.

And how do i do this?  I not a techie so this is a learning curve for me.

Thanks SashaE.