Owing the IRS money does not automatically exclude you from being eligible for all mortgages. You may still be able to obtain a mortgage depending on the lender. Most lenders will require that you satisfy the IRS debt through the loan. Usually the lender requires this because they dont want to have teh IRS garnish your bank account and then as a result miss you paying your mortgage. However because you have an IRS debt you may receive a higher interest than borrowers who dont.
It would be worth while to call a mortgage lender and apply for a loan and see what they tell you. Usually if you get turned down they will tell you why and what you can do to get approved in the future.