(IRS properly gave notice to plaintiff of his responsibility as a "responsible person" to pay payroll taxes (over $50,000) for company that is now bankrupt (plaintiff was Secretary/Treasurer of the Company); plaintiff signed Form 2751 consenting to the assessment and collection of the taxes; Form 1153(DO) is not exclusive method for providing notice to taxpayer and I.R.C. Sec. 6672(b)(1) does not describe specific method of notice to be used).