It's your RAM.
You have 1 GB of ram and recommended is 2.
If you have little ram AND only 4GB left on your hard drive after installing it, then those are both factors that cause you to lag.
Check your connection too. LAN, Wireless?
I cant see how my graphics card can be bad as my friend said that it is much better then what is needed. I will upgrade my RAM and get an external hard drive most likely.
I have the same problem, but yet i have 2gb Ram, and its a Alienware computer, its suppose to run it without any problems, but i tryed reinstalling it but yet it is still lagging a hell of alot,
Windows 7 home 64bit
Intel Core i5
2gb Ram
NVIDIA GeForce GT 335m
Recommended from experience:
4-6gb of ram (not joking)
3ghz+ quad core processor OR a six core (any)
nVidia GTX 4 Series (470 or 480 for optimal performance)
RAM $100 for a stick of 4gb ddr3
Processor about $200 for a phenom II x6 @ 2.8ghz
Graphics card is about $240