must change once a month (for maximum thermal dissipation, and for OC freak) or at least once 6 months if u are lazy.

*capalang RM3 (or less), the white colour one, which looks like toothpaste.  is recommended for u. no need buy expensive one, as it not worth at all. even though u are a super oc freak or oc noob.

direct contact.currently conroe setup no use any thermalpaste.

last time used to have nano fusion,as5,MX-1,and a lot,i still vote for MX-1 and toothpaste,no kidding,they can transfer heat like tim.

u can use double-sided tape from 3m 

no just kidding bout the last paragraph, well u can get the thermal adhesive from artic silver i tink...moderno got sell...alot of other places also selling =)