I'm building up a newish track frame and its got a 70mm bottom bracket, but for some reason the bottom bracket i have for it just wont work. I tried installing it but the threads will not start. Almost seems like the cups are too big for the bottom bracket, but English cups just fall right through. Am i doing something wrong, or do i have the wrong parts?

Don't force 'em in. Take the bike to your LBS. Is there paint in the threads?

Sounds like you have an italian bb. 36x24 is bigger than 1.37x24 english. So you will get the effect of cups "falling through", if the cups are english and your bb = italian.

Yeah, The cups i have are italian and the bottom bracket is italian, but the cups seem too big. So I tried some sugino 75 cups and they fell right through.

Italian has right hand threads on both sides, are you turning the cups in the correct direction?

You may be threading it in the wrong way, Italian BB's are the only ones that can be threaded in backwards. Make sure you start on the drive side and screw it in toward the non-drive side.