Here's the citation for Harriet.
http://"Australia, Births and Baptisms, 1792-1981," index, FamilySearch (https://familysearch.org/pal:/MM9.1.1/XTXF-ZQS : accessed 17 January 2015), Harriet Foster, ; citing , , TASMANIA, AUSTRALIA; FHL microfilm 1,368,245.
You can borrow the film and have it sent to your nearest Family History Centre (LDS Church) and then save the image for your files.
Thankyou so much Wayne for your help. unfortunately following that line last year, i found a death certificate for this Harriet, she died at 7 years old and on my Harriet's marriage certificate she was 17 so was born in 1852. She is an elusive woman