I made about $5000 mowing lawns in 2008. I do not have any tax forms and have no way of obtaining them. How do I account for this on my tax return?

You must report your income even if you do not have any tax form.
You are self employed or independent contractor. You must file your tax return if yourself employed income is $400 or more. You will report your income and expenses on schedule C or C-EZ (Form 1040). Then you put net income (or loss) on line 12 of Form 1040. This income is subject to SE tax at 15.3% (this is shown on line 57 of Form 1040). Half of SE tax is deductible on line 27 of Form 1040. Read: Your U.S. Tax Return: Tax Filing by Self Employed Sole Proprietor or Independent Contractor