First of all, a thermistor costs like $0.40 a piece if you buy 10 or 20 at a time so even if you can't figure out the factors, not big deal, buy some that come with spec sheets. If you want to determine the spec of your blue thermistor, you need to measure at least two temperatures., 25DegC and something like 80DegC if it's not too hard to do.

Set 25DegC and measure resistance gives you R1, then set at say 85DegC and measure resistance again you can solve for B.

Here is my article on how to use a thermistor:

http://liudr.wordpress.com/2011/02/10/measure-temperature/