A PR visa doesn't require a job offer. Australia is one of the few countries that allow a migrant to apply on a prospective basis.
The ACS handles skill assessments for IT professions. The relevant page is at:
http://www.acs.org.au/index.cfm?action=load&temID=skillassessment
In particular, there's a handy "am I eligible" guide here.
http://www.acs.org.au/public/ska/docs/Summary%20of%20Criteria%20-%20V5.pdf
Given your background, your options would either be getting yourself assessed in lieu of education (Recognition of Prior Learning), which would need eight years work experience, or get a suitable professional qualification (some of the MS certifications count, see the link above), and five years experience. I'd suggest the latter, but it depends on how much it'd cost to do.