Adding New Rows To Grid Decreasing Performance of Web Page

Hi All,
 In my application, There will be customer list in dropdown, when we select any customer then projects assign to that customer will be displayed dynamically(each project will be having check box to select the projects) and there may be different no. of projects for different customer.
If we select these projects and click search button, employees present to all projects will be displayed to the grid view.
And we have to add new employees  for the projects by adding new rows dynamically to the grid view(which contains employees list as dropdown list  and other columns with text boxes).
I am able to add the new rows to the grid view but what is happening is after adding new rows to the grid the browser getting slow,  when i am trying to select drop down lists or click on any place inside the browser then the page is not responding and after some times the browser getting hanged.


Please sugges ...