Need help joining different files to make a mixed video

[battleangel3222]

Hey Guys, I was asked to make a video of some...well umm pr0n and anime together, I can split the files i want, but joining them is a problem because resolutions and stuff need to be the exact same...can anyone tell me a way i can join them or convert them all to the same thing so it will work? thanks

 

[anotherguy159]

Adobe Premier