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?
One of possible solutions:
Install previous Ubuntu version (for instance, starting from 9.10) then gradually upgrade to the latest one. In many cases it works fine. Anyway you will see how perfomance is changing from previous version to next one.