Ajuda com variavel

Front-end
#1 

<TABLE align=center width=600 border=0 >   
  <TR>       
    <TD class="toleft" nowrap>   
   <select  name="arrDate_day" class="vsel" onchange="if(self.gfPop)gfPop.updateHidden(this)">   
   <script>document.write('<option value="-">-');for(var i=1;i<=31;i++) {document.write('<option value="'+i+'">'+i)}</script>   
   </select> /   
           
   <select name="arrDate_mon"  onchange="pegadata()" class="vsel" onchange="if(self.gfPop)gfPop.updateHidden(this)">   
   <script>document.write('<option value="-">-');for(var i=1;i<=12;i++) {document.write('<option value="'+i+'">'+i)}</script>   
   </select> /   
           
   <select name="arrDate_year" onchange="pegadata()" class="vsel" onchange="if(self.gfPop)gfPop.updateHidden(this)">   
   <script>document.write('<option value="-">-');for(var i=1980;i<=2030;i++) {document.write('<option value="'+i+'">'+i)}</script>   
   </select>    
           
        <INPUT name="popcal"  onclick=" if(this.blur)this.blur();var fm=this.form;if(self.gfPop)gfPop.fPopCalendar(fm.arrDate,null,null,fm.arrDate_year); " type="button" value="..." class="vbtn">   
   <input name="arrDate" type="hidden" value="">   
      
<TABLE align=center width=600 border=0 >
  <TR>    
    <TD class="toleft" nowrap>
   <select  name="arrDate_day" class="vsel" onchange="if(self.gfPop)gfPop.updateHidden(this)">
   <script>document.write('<option value="-">-');for(var i=1;i<=31;i++) {document.write('<option value="'+i+'">'+i)}</script>
   </select> /
        
   <select name="arrDate_mon"  onchange="pegadata()" class="vsel" onchange="if(self.gfPop)gfPop.updateHidden(this)">
   <script>document.write('<option value="-">-');for(var i=1;i<=12;i++) {document.write('<option value="'+i+'">'+i)}</script>
   </select> /
        
   <select name="arrDate_year" onchange="pegadata()" class="vsel" onchange="if(self.gfPop)gfPop.updateHidden(this)">
   <script>document.write('<option value="-">-');for(var i=1980;i<=2030;i++) {document.write('<option value="'+i+'">'+i)}</script>
   </select> 
        
        <INPUT name="popcal"  onclick=" if(this.blur)this.blur();var fm=this.form;if(self.gfPop)gfPop.fPopCalendar(fm.arrDate,null,null,fm.arrDate_year); " type="button" value="..." class="vbtn">
   <input name="arrDate" type="hidden" value="">
     
onde isso resulta um calendario com 3 selects um pro dia mes e ano quando tu escolhe ele preenche os 3 select com o dia mes e ano escolhido

porem quero fazer isso em 1 input text
<td><input type="text" name="data" size="50" value="" /></td>

passar o valor contido nos 3 selects para o input alguem ajuda
#2