javascript and asp.net

Question

i created a rollover in java script which is interactive and allow user to choose bewteen countries -5 countries - represented in images, what i need is when the user click on an image a server side code should be executed to update the datagrid according to the country selected, so i need to add anycode in a javascript function -which will be called when the user click on the image(onclick)- to call this server side code .

i hope i could make it clear.
need urgent help

Thanks