These are called as OEM processors. These processors are not sold in the retail market. They are directly provided to leading notebook manufacturers and their ODMs. Over the past couple of years, due to ever increasing sales of notebooks, Intel fails to keep up with the demand. So while their Core duo T2300, T2400,.. and similar lot were almost out of stock, they provided the first of the kinds you are talking abt in the forum like T2050 & T2250. It's like these processors are shipped to manufacturers just to keep a particular family of processors going when something better ( Core 2 Duo) are selling or just around the corner. Similarly with T5300, since the second generation mobile Core 2 Duo's with 800MHz FSB will be out any moment.
Well, as for those two proccys- they are more or less similar. Not much difference.
Hope this helped!
Edit: T2350, T2060 & T2080 Pentium DualCore are also similar.
