Music copyright etc.

Hi.

Could anyone tell me whether it is possible to use recorded music (ie: cds ) as backing music etc in original pieces? Do we need to sort out anything to do with copyright, because I imagine we do, but being slow to get around to things, completely forgot about it until now. At the moment the only plans we have for the piece is for youthfest if that has any influence...

Will it be too much hassle to use "popular" music? Should we embark on a search for local bands with original music?

Any suggestions and shared knowledge is much appreciated, because we've been procrastinating for too long!

thanks,
Rebecca