Koss,

Unfortunately, the tax assessed value may or may not be close to what the true market value of the home is today. There are many factors that influence this, from the neighborhood which the property is in to the condition of the property and other factors. The best way to determine what today's market value is (what you might be able to buy/sell the home for today) is to have a real estate agent perform a comparable market analysis (CMA). This CMA will take into account those various factors as well as what other properties are currently for sale & have sold recently in the immediate area. Personal circumstances may affect the home's true market value as well. Let me know if you have further questions about this, I'd be glad to help!

That's a tough question to answer without more details, but typically a tax assessors value is less than what an actual appraisal value would be. It might be safe to say it could be valued close to the $140k because the height of the housing market was 2006, and now that the market has declined so rapidly, the appraisal value will have dropped.
The best way to determine how much a home may be worth is to look at similar home sales within a 1 mile radius of the subject property. Look at things such as square footage, style, updates, etc...