If I want to dispute an item on my credit report, what is the procedure I should follow? Do I have a good chance of getting errors eliminated? Do the credit reporting agencies have a limited mount of time in which they have to verify the debt and provide me with proof? Any help would be useful. Thank you in advance.

Go to the website for the company that provided the report. They will have info there on the process. Links for all three follow.
Transunion
TransUnion Personal: Submit a Credit Dispute – Online, by Phone or by U.S. Mail
Experian
Credit Report and free credit score at Experian.com
Equifax
Equifax Online Help: How to Correct Errors on Your Equifax Credit File