If you're hoping to use the ISIS unit as your immobiliser, make sure it complies with ADR 82. Scroll down this page for more info.
http://www.infrastructure.gov.au/roa...dr_online.aspx
Failing that, I can recommend the Mongoose M80 for $200 which is ADR approved with a 3 point immobiliser, shock and microwave sensors plus boot/bonnet/handbrake kill switches and a well designed keyfob.