You cannot upgrade a netbook. If you want better performance, then you need to buy a laptop that actually has the ability to play games which generally varies based on the cost of the laptop. The more expensive it is, the better it's gaming potential, but you also need to look at the laptop's specs. An $800 can be more capable of playing games than a $1,200 laptop. It depends on the specs and the consumer segment they are being marketed to.
TF2 and LF4D2 are based on Valve's Source Engine which has been in existence since 2005. Valve have made tweaks to it since then for later game releases, but the Source Engine has extremely low requirements compared to more resent game engines. You should be able to play any game based on Valve's Source engine which includes Half Life 2, Portal 1 & 2, Vampire The Masquerade: Bloodlines, and probably the upcoming Counter-Strike: Global Offensive the official sequel developed by Valve to the community developed Counter Strike mod for the original Half Life 1 game engine.
The AMD E-300 and the integrated Radeon HD 6320 graphic core are really, really slow compared to CPUs found in current laptops. I would say that the AMD E-300 would probably be equivalent to an AMD Athlon X2 CPU running at 1.0GHz to 1.2GHz. The Radeon HD 6320 is probably equivalent to a Radeon HD 4550 desktop graphic card at best.