i want to autogenerate my empid

Question

I have created form empdetails where employee will enter his details like name,address etc the empid will be generated automatically in my case empid starts with usr0001 i have created table with empid column made it as identity
when user clicks on the this form i have textbox empid this textbox should display this auto genereated id. like usr002

How can i do that i'm using sql server 2005 in asp.net using c#

Can any1 help me on this.