I received an AUR tax bill for 2007?

The bill is for $1800, and it does appear that I made a mistake because I also under-reported the amount of income tax withheld (and they corrected that too).

If I filed bankruptcy in that year, should I send them that info? (I am not CURRENTLY in bankruptcy because it has been 2 years).

Also, if I send them a check for, say, a 60% portion of that, do you think they would accept it?

AUR is interchangeable with CP2000. CP2000 is the more common name for the mismatch letter.

As for bankruptcy, you can't include taxes in a bankruptcy until they are at least years stale. The 2007 tax return was filed in 4/15/2008 and could not have been included in a bankruptcy until 2011.

As for settling, OIC isn't likely to be considered unless you owe at least $10,000 and are broke.

2007 income tax was not previously included in the bankruptcy, so you can't add it in now.
IRS will accept the 60%, and then complete form 9465 installment agreement request to set up an installment for the reminder 40% plus interest and penalties. Or call IRS at 1-800-829-0922 to set up a 30, 60, 90 or 120 day extension to pay. Or write IRS a letter when paying the 60% and request either an extension or installment agreement. When you file your 2009 tax return and you still owe and are due a refund for 2009 the refund will automatically be offset to the debt.
Good luck!

If you owe $1800, they will not accept less. If you pay them 60%, you will get a bill for the remaining 40% (plus interest) in a few weeks.

No idea what "AUR" is, but the general rule in the US is that tax debts that are less than 3 years old cannot be included in bankruptcy. And even if your debt was that old, if it was not included in the bankruptcy action that constitutes a constructive ratification of the debt so you must pay it.

Most tax authorities will accept nothing less than payment in full if there's any possibility that you can pay it off (along with the penalties and interest set by law) in 5 years or less.

Without knowing all of the details in the notice and the tax return(s) in question there's no possible way to advise you what to do. If the assessment is correct, pay it. If it is not, file an amended return showing what it should be and pay that amount with the amended return.