Form fields - textboxes - ecluding one if something input in another

Apologies if this has already been answered - had a look and didn't find anything similar.
 
I've created a form where people can order catering. there's often confusion with tea/coffee (we supply) and hot water urns (bring your own teabags). I want users to:
 
1. not be able to put anything into "hot water urns" field if they have input anything in "tea/coffee" fields
 
2. get an alert saying that they don't need hot water urns if they take "coffee/tea"
 
3. get an alert reminding them to bring their own supplies if they go for "hot water" option
 
Using Acrobat Pro 8.1.3
Not very savvy with custom Javascripts but could copy and paste it:)