marainwa,
glad to see your got your x10 stuff. i sure you will get the help you need for the 3way switches. your remote should have the ability to send x10 commands to the ir543. see page 100 of your remote's user manual. or click on the link on this page:
[Link: iq.sony.com]
to get your manual online.
after you set up the x10 on your remote, point it at the ir543 and press "1" "0n"
if you see the red LED light up on the ir543, you've got it.
good luck.