Duemilanove & WiFly direct connection

Hello and sorry for a basic question, but after hours of searching I seem to only find conflicting info.

Can I plug a Sparkfun WiFly shield directly into a Duemilanove board? I’ve seen photos of this but also advice about linking the 3.3v supply from the board to the shield, and not connecting 5v directly.

I guess an even simpler question is: do specific shields only connect the necessary pins to the device on the shield, such as RN-131C? So you can stack any number of boards in any sequence without problems, as long as the shields are for different purposes (Digital IO, Analogue, PWM etc)?

I don’t want my first experience with Arduino to be my last. Thanks.

Anyone got an answer? I still haven’t powered it up yet.

19/Nov/2011: Still waiting for a reply if anyone is on this forum