The County has put a lien on my house. I have been unable to pay the taxes for last year and may be unable to pay them this year. How long before they can legally sell it? Is there a way I can stop it from being sold other than paying off the lien in one lump sum?

That depends on local laws. So you need to check with your county. Does the property have a mortgage?

Like Scott said, it depends on your local laws. I know someone here in Wisconsin who hasn't paid her property taxes for the last 3 years and they still haven't taken the house from her(knock on wood).

As far as I know, you don't need to pay off the lien in one whole payment, but you do need to pay as much as you can, as soon as you can.

If you can not make proper arrangements with them, to repay, normally they do not put a lien until it is two years behind, but after two years are due most areas sell the property, so you will most likely need to pay last years tax in full before this one comes due.