Creating indexes?

What is the best approach for PostgreSQL when creating indexes? E.g I have two fields in a table that I want indexed,
isit best to create one index 
combining the two fields or creating one for each field? If I create one for each field, will the search when using
bothfields be slower that a 
combined index?


Regards,

BTJ

--
-----------------------------------------------------------------------------------------------
Bjørn T Johansen

btj@havleik.no
-----------------------------------------------------------------------------------------------
Someone wrote:
"I understand that if you play a Windows CD backwards you hear strange Satanic messages"
To which someone replied:
"It's even worse than that; play it forwards and it installs Windows"
-----------------------------------------------------------------------------------------------