Hi,

I am currently on a 4-year Temporay 457 visa (since Nov 07) and was on a Working Holiday Visa prior to that (from Jan 07). I would like to apply for PR.

a) how long do I need to have been here before I can apply for PR?

b) what are the differences between ENS and skilled migration? Which is the best/easiest route to take?

Thanks

You can apply for a permanent residency visa as soon as you are eligible - the question is therefore when are you eligible => there is insufficient information in your posting to answer.

Maybe start by having a look at the eligibility requirements - those for the ENS are here:
http://www.immi.gov.au/skilled/skilled-workers/ens/eligibility-employee.htm

If you think you might require some formal assistance please feel able to telephone us on Melbourne number 03 9935 2929.

Best regards.