I'm not sure which lawn mower model you have, but you can check out page 19-21 of [link|http://dl.owneriq.net/1/19d03548-bf16-4335-8f25-6d81493377f7.pdf|this Operator's Manual PDF] for Murray model 96012007200.
Other [link|http://lawnandgarden.manualsonline.com/manuals/mfg/murray/murray_lawn_mower_product_list.html|Murray operator manuals] also exist on that somewhat-spammy site, but unfortunately there's no iFixit guides for them (yet!).
Perhaps you can start a Murray repair guide for the drive belt when you perform your repair? :)