Fw: application compatibility with Oracle

hi,

i am looking to write applications in .net
( using odbc or some faster but similar compatible tech.)
that could run with
PostGreSql OR Oracle
with minimal changes.( any other database server compatibility would be a bonus !)

for this i need to know
what database constructs and
programming techniques
i can use so that the application would run with either PostGreSql or Oracle.

any advice in this regards is greatly appreciated

TIA

regards
-adivi