|Well if you want something with performance then avoid the Core 2 Duo SU7300.|
The Turion II is based on the Phenom II architecture and the M520 is equal to that of a Desktop AM2+ Phenom II based, Athlon X2 5000+ performance.
The Core 2 Duo T6600 is equal to that of a Desktop LGA775 Intel Core 2 Duo E4500 performance.
The Core 2 duo T6600 due to the larger L2 cache has the slight advantage over the Turion II M520, but not by much.
The first laptop on your list the Dell 1570 Laptop is out of the question for gaming and performance. The processor itself is too slow for that.
The HP DV7-3020sa comes with a Nvida Geforce GT 230 gpu which is equal to the Nvidia Geforce 9600GT gpu in performance and is considerd still a decent mid range gaming gpu.
HP DV6-1340sa comes with a ATI Radeon 4530 which is considered a low end bugdet gpu and isn't ideal for gaming.
The HP DV7-3020sa has the big advantage over the HP DV6-1340sa in graphics performance.
The HP DV7-3020sa is the best one out of the 3. It has the best performance overall to suit your needs.
Iron Sharpens Iron.