Stock footage using real fire is the best option, provided you can find something that looks like what you want. CG fire, especially create from AE still lacks realism.
You may want to start your search at the COW's new Stockyard site ->
http://stockyard.creativecow.net/
HTH
RoRK
Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer