How to display a checkboxlist or a radiobuttonlist inside a html select control?please very urgent..

Question

Hai all,
iam stucked with a problem.
i want to display a checkboxlist or a radiobuttonlist inside a html select control.
similar to the msdn search.(whenever we click on Language or Technology or ContentType) a checkboxlist is generated inside the select control.
please suggest me how to do that.please very urgent.......
Thanx in advance guys...