How to calculate power rating of resistors for pi attenuation?

Hi,
i want to use a pi attenuator to make 30dB attenuation. the point is that this attenuator should be capable of handling 50watt. i want to know how to calculate power rating of each of pi resistors? in addition should they have special matter?
thanks

http://www.microwaves101.com/encyclo...nuatordiss.cfm

IanP
:D

tnx!
it was helpful.