What is the song playing in the P Diddy diet pepsi commercials and who is the band?

The song is "Fantastic Voyage," as performed by Coolio. A well-known
earlier version of this song was done by the funk group Lakeside in
1980.

"Truck" by DDB New York for PepsiCo... 

 Soundtrack/Song 
 Fantastic Voyage...

 Actor/Celebrity 
 Eva Longoria, P. Diddy"   

OsUniversitarios: Ótimo comercial
http://www.osuniversitarios.com.br/modules.php?name=News&file=print&sid=351

"Best use of song - Diet Pepsi's Stayin' Alive ad of the guy walking
down the street edges out the P. Diddy ad's use of Coolio's Fantastic
Voyage."

Greeley Tribune: Super Bowl ads deliver the goods
http://greeleytribune.com/apps/pbcs.dll/article?AID=/20050207/NEWS/102070036

"P. Diddy Diet Pepsi / Coolio - 'Fantastic Voyage' 
(Song was originally done by old school rappers / Lakeside)"

Hand Coding: Songs in Commercials
http://www.handcoding.com/archives/2002/08/29/songs-in-commercials/

My Google search strategy:

Google Web Search: "diet pepsi " "p diddy" "fantastic voyage"
://www.google.com/search?hl=en&q=%22diet+pepsi+%22+%22p+diddy%22+%22fantastic+voyage%22

I hope this is helpful! If anything is unclear or incomplete, please
request clarification; I'll be glad to offer further assistance before
you rate my answer.

Best regards,
pinkfreud

Extremely quick and thorough answer!  Saved me a lot of time.