Presuming that you filed a joint return ("when he did our taxes") then there is no way for you to amend the 2006 return to include the inadvertently omitted income without his signature on the joint return. So, unless it is your plan to slip the tax papers into other items he is signing in the hope he does not notice you will have to confess to the omission.
You will use Form 1040X to include the income and recompute the tax due. You have three years from the original date filed to submit the Form 1040X. Perhaps you should wait to amend the return until after you clean out your briefcase and any other places that could contain return information (half kidding there). Or, you may wish to compile all of the 2007 information and then present both the new complete and orderly information and the omitted prior year item.
Since you are including additonal income you will likely have a balance due (and some interest); but should be able to plead for mercy and request abatement of any penalty, if you have a good history of compliance.
I hope this helps. Best wishes on the confession and apology to your husband.
Hello Craig !
Happy New Year to you and yours, as well. Thank you for the opportunity to be of service.