T4200 vs T5870

Hello and welcome to the forums  
The difference between DDR2 and DDR3 isn't much also 3GB vs 4GB doesn't make a lot of difference either,the difference between the CPUs is that the T5870 has 2MB cache whereas T4200 has 1MB which won't make a huge difference,so overall the difference between the notebooks isn't much.
If the other specs are the same and the price is the same too then go for the Lenvo model which has a slightly better config