Not my Debt

i recently got a letter from a collection agency regarding a debt that i had no knowledge of. how do i go about disputing this debt and is there any time limit governing disputes? if so, am i without recourse if the time to dispute has passed? if i am able to dispute the debt what follows?

No, time hasn't run out on you. Send them a certified "cease and desist" letter also requesting validation of the debt. With help writing one of these letters, do a search on the net using "cease and desist" and you should be able to find some good examples on how to write it.