You could use a ListBox or GridView to accomplish this.
It's up to you which you prefer.
I wouldn't recommend opening another window with selected employee but it's possible. You'd store the employee selected in session so that it could be accessed in another aspx page....or pass it to the other page in the URL....when you clicked the button you'd use JavaScript to open a new browser window, calling the aspx page.
The reason I don't recommend displaying the selected employee in a pop up window is because I'm sure that your next step will require updating the parent window after the child one closes...and this is very annoying (trust me).
I would recommend creating a Web User Control instead so that you can place it on the same page. When the user clicks the button to display employee information the control would be made visible.
Using CSS you can make things appear to float on top of the rest of the page. You can even let the user move it around by using the free
DragPanel extender.
Really, this solution will save you a lot of headache.
But, you may require the child window to open...
Why don't you give this project a try and when you get stuck on something ask for help at that point and we'll be right here to get you through your problems.
-Frinny