Yes, the adoption credit is still available for the 2010 tax year. If you finalize your adoption in 2010 you would claim the credit on your 2010 return. You may also claim expenses you paid in a prior year before the adoption became final.
If you do not have a high enough tax liability, then as you pointed out you may not be able to take advantage of the entire credit, as it only reduces the amount of any tax you owe. That being the case, you could certainly take a lump sum distribution from your 401k plan and your adoption credit would be used to reduce the taxes you owed on that distribution. The adoption tax credit is simply used to reduce any federal income tax you owe, regardless of the source of your taxable income.
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Thank you Daryl