be worth your money to hire a tax man this year. You can file an amended form for last year, but it has to be done correctly.
You don’t generally deduct investments. You pay taxes on the income that they generate. There are special treatments for oil and gas wells but you’d be well advised to seek professional assistance (CPA or tax attorney, not Block or Hewitt) as the rules are complex.
If this is for tax year 2005, you must file an amended return on Form 1040X.