You have to check the core of your CPU to know your exact stepping. I would not recommend doing this unless you are really serious about over-clocking, you are changing or reseating or reapplying thermal compound (or AS2 of course) to your heatsink, or you are worried your retailer ripped you off and OC'ed a lower version t-bird thru the BIOS.
Basically, your t-bird core will tell you all this info, along with the stepping.
If it is a 1.2 gig t-bird you will see the following:
A1200AMS3C
XXXXXzz01YYzz
Xzzzzzzzzzzzzzz
The letters represented by X are commonly referred to as the CPU's stepping. YY will tell you the week it was made, which is also a factor.
Chiz