set theReply to display dialog "Hello World" buttons {"Foo", "Bar"} default button 1
if (button returned of theReply) is "foo" then
open location "http://www.foo.com"
end if
if (button returned of theReply) is "bar" then
open location "http://www.bar.com"
end if
all the interestingly quirky classes and events are in the "Standard Additions".
Look for it by choosing "Open Dictionary" in Script Editor.
also this is quite an interesting event:
choose URL showing {Web servers, File servers} without editable URL