Sounds like the installation may have made changes you didn't count on, like setting some things to run at start that may not need to and resinstalling programs that you may have uninstalled.
Try going to "Start" and then search for "msconfig" (without the quotes). In there, click on the "Start Up" tab and check the list to make sure it is only loading things you want it to when Windows starts.
NOTE: Be careful in there not to turn off anything or remove anything without being completely sure of what you are doing.
Then go to "Control Panel" and then "Programs" and uninstall anything you don't want/need. Again, be careful of what you remove. Don't remove anything you are not 100% sure about.
You may also want to update all your drivers.
After all this, restart the computer (turn it off and back on) and it should run better.