Form Fields Validation

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Hello everybody!<BR><BR>How can I validate a field from a form to see if it's value?<BR>this is what i have done:<BR><BR><form method="POST" runat="server"> <BR><table><BR><tr><BR><td><asp:label id="lNome" text="Name:" runat="server" /></td><BR><td><asp:textbox id="tNome" size="30" runat="SERVER" /></td><BR></tr><BR><tr><BR><td align="center" colspan="2" ><input type="button" onclick="Validate()" value=http://aspmessageboard.com/archive/index.php/"Validate" runat="server"></td><BR><tr><BR></table> <BR></form><BR><BR>and the function:<BR><BR><script language="vbscript" runat="server"><BR><BR>Sub Validate()<BR><BR> if tNome.value = "" then '--What Can I use here??--<BR> msgbox ("OK")<BR> else <BR> msgbox ("KO")<BR> end if <BR><BR>End Sub<BR><BR>------------<BR><BR>Thanx in advance<BR>bRunoFskIhttp://shop.barnesandnoble.com/booksearch/isbninquiry.asp?salesurl=Ishop.barnesandnoble.com/booksearch/isbninquiry.asp&isbn=0672321432&displayonly=excerpt<BR><BR><BR>For Javascript , http://www.4guysfromrolla.com/webtech/102798-1.shtml