Head of household
From what you say, I believe you do not qualify for head of household status for 2000.
You can file as head of household if you otherwise qualify and if you are considered unmarriee on the last day of the year.
UnderYou are considered unmarried on the last day of the year if you are legally separated from your spouse, according to your state law, under a divorce or separate maintenance decree. You fail to qualify for this because you are not separated under a divorce or separate maintenance decree.
However, you would also considered unmarried on the last day of the tax year if you meet all of the following tests.
1) You file a separate return; 2) You paid more than half the cost of keeping up your home for the tax year; 3) Your spouse did not live in your home during the last 6 months of the tax year; 4) your home was the main home of your child; and 5) you must be able to claim an exemption for the child.
From what you say, you qualify under all but number 4, since your spouse did live in your home during the last 6 months of the tax year. Therefore, unfortunately you do not qualify for head of household status for the year 2000; however, if you remain apart, you would qualify for the year 2001.