You should notice on the visa in your passport or on the approval email you should have received the following text:-

granted a Subclass 457 visa.  This visa provides for multiple entries to Australia and is valid until the date specified above.
 
Also on http://www.immi.gov.au/skilled/skilled-workers/sbs/index.htm

after entering Australia, have no limit on the number of times they travel in and out of Australia.
 
Depending upon your nationality, check with the New Zealand Govt. about their visa entry requirements
 
http://www.nz-immigration.co.nz/visitor-visa-pack.html
 
For Australian Migration Agent information
http://www.themara.com.au/
 
www.australiantrades.com