Help needed in performing validation

hi friends

i should do server side validation on two controls
by making use of if condition in aps.net 1.1

i should not use any validation controls instead i should make use of
if..else condition for performing validation..
i have a textbox and a drop down list box..
text box ha new entry
dropdown list box has selected items present in it
now i should write the coding for validating as such user
can enter new one or can select one...

please suggest me the solution for this

regards,
gayathri

You can either use custom validation where u can pass ur custom validation function , where
u can write ur validation code for text box or listbox.

or

You can validate this two control on form load. where u can check textbox entry or listbox selection
because envery time when page is post back it will check the control validation .