when i was going to create an account on mania planet it said the e-mail address was already in use. i vaguely remember trying to set up one. but it was so long ago i don't remember my username and password. any ideas?

Do you mean on ManiaPlanet Forums?

Well I have to have a maniaplanet account and a mania exchange account and link them in order to post tracks right? because thats all i really want to do.

That's correct.

If you're having trouble (because of forgetting your password) logging into player.maniaplanet.com you should contact Nadeo support.

Once you have that resolved, you can try again to connect your maniaplanet account to your mania exchange profile here so that you can use the site.