Question: I'm running ubuntu lucid lynx on the following config:

* 2GB DDR2 Ram
* 1.50Ghz Core2Duo
* Nvidia 128MB 8400GS GFX Card

Due to some reason the entire operating system feels laggy. The window manager, firefox and rhythmbox and almost all apps feel a bit slow. There is almost a second time lag between the time I press ctrl+T to open a new tab on firefox and the time it actually opens. This site itself renders in frames and the scrolling up and down is a pain.
Rhythmbox takes 1 sec to maximize and minimize and I cant even dream of a changing the workspace.

My question is if Windows 7 is running perfectly on my comp why isnt Ubuntu? I really hope there is a way because I would love to ditch windows and move over to linux full time.

Is there anyone for whom ubuntu works as it should while running a similar config?
Thanks

Answer: 
I suspect it is the graphics card slowing you down (it is a low end model) - what driver are you using for the card?

You should install the Nvidia restricted driver for the best possible performance.

Also you mention no issues on Win7 - does it work on the aero interface OK?
It is most likely due to a bad VGA driver. You can easily confirm this by selecting Ubuntu 2D before you log in by pressing the button next to the password field. If that gives you a fast desktop, then you need to get some drivers for your VGA. If you need help doing that, you should open a new question.