You can wire it two 2 ports from that one set of 3. I wrote some code for that sensor and it works if one of the pins is in port 1 or 2. I am working now to get ports 3-6 working, but with no luck.
Basically what you have to do is send a pulse on a digital output (set one of them to 1 for a couple of seconds) then you wait for an input, which is where you use an interrupt and a timer to time the pulse. Take a look at the datasheet for that sensor
http://www.parallax.com/Portals/0/Do...-PING-v1.4.pdf
and if you would like I could upload my code that works with ports 1&2.