Okay, here is what I have found. Now, I am not 100% certain about this, and if you are dead serious about purchasing a home at the foreclosure auction you should consult a RE attorney to be certain.
As long as the liens are junior to the 1st mortgage lien that is foreclosing: i.e. The mortgage was recorded in 2006 but the tax lien was recorded in 2007 it should be wiped out just like any other junior lien. If it was recorded before, just don't buy the property, it will be a colossal PITA to fix it, and you might have to pay all or some of it.
A state lien that is junior is wiped out immediately after the trustees sale.
A Fed tax lien that is junior is wiped out after the 120 right or redemption period. If the IRS contacts you within the 120 days, you might have to negotiate the lien with them. From what I have read, most just wait out the 120 day ROR, and then sell the property. If you are not selling the property, then after the 120 ROR you would need to contact the IRS to verify it has been removed.
IMHO, I would just avoid any house with a tax lien. Sounds like too much trouble to me, and there are plenty of other opportunities out there.
A property tax lien is senior to everyone but gawd himself.