I actually do this for a living.
If you check Publication 15 at IRS.gov, you'll see that there must be more factors at work here. I'm thinking that even if your company put you in the payroll system correctly, you would still owe something. There is a difference between the tables used to calculate the withholding for single vs married people, but the difference is not going to be $4000. Most likely, you claimed too many excemptions. Also, as others have stated, the tax liability is yours. No one else's. You should (in the future) check your paystubs each week to ensure that you have enough withheld. Most paystubs will tell you year-to-date totals. If you have 4000 worth of liability this year, you want to make sure you're at least that much ahead next year.
Unless you get married, have triplets, and buy a big house.
But if your personal life doesn't change too much, be sure to have mroe withheld.
His: 1996 ZJ, 4.0 Selec-Trac
Hers: 1993 ZJ Woody 5.2
Ours: 2004 Chrysler Town & Country Touring. Sweet.
Previous Jeeps: 86 XJ, 92 XJ, 95 YJ, 87 YJ