Got some time to give you a good sample:
First you download a calendar applet here you can do this:
Here is the code (you need IIS to run the asp page)
The html page:
<script language="javascript">
window.focus();
</script>
<table border="0" cellpadding="0" cellspacing="0" width="100%">
<form name=beamer action=beamerlist.asp>
<tr>
<td bgColor=#98cecb onclick="window.open('testdate.asp?CtlName=1&startdate=' + strt1.value , 'MSWindow', 'menubar=no,width=350,height=250');" title="Click here to change the start date/time" style="cursor: hand">
<label id=starttimedate1 name=starttimedate1>08 December 2001 16:36</label>
<input type=hidden value="08 December 2001 16:36" name=strt1 id=strt1>
</td>
</tr>
<table>
The asp page:
<script language="JavaScript">
window.focus();
</script>
<script language="vbscript">
function seeDate()
i = document.tL2.getDate()
window.opener.document.forms(0).elements("strt<%=Request.QueryString("CtlName"

%>"

.value = month(i) & "/" & Day(i) & "/" & year(i) & " " & thetime.value
window.opener.document.all.item("starttimedate<%=Request.QueryString("CtlName"

%>"

.innerText = Day(i) & " " & monthname(month(i)) & " " & year(i) & " " & thetime.value
window.close()
end function
</script>
<center>
<applet code=tcaldate.class width=160 height=170 NAME="tL2" ID="tL2" MAYSCRIPT>
<param name=link value="%M/%D/%Y">
<param name=script value="javascript:seeDate()">
<param name=target value="_none">
<param name=startsunday value="0">
<param name=font value="Arial">
<param name=fontsize value=12>
<param name=fontstyle value=1>
<param name=bgcolor value=13684944>
<param name=bgcolor2 value=14737663>
<param name=bgcolor3 value=400>
<%
if request("startdate"

<> "" then
tme = request("startdate"

tme = mid(tme,1,len(tme)-6)
tme = month(tme) & "/" & day(tme) & "/" & year(tme)
else
tme = now()
tme = mid(tme,1,len(tme)-6)
tme = month(tme) & "/" & day(tme) & "/" & year(tme)
end if
%>
<param name=current value=<%=tme%>>
<param name=t_col1 value=400>
<param name=t_col2 value=8421520>
<param name=t_col3 value=14737663>
</applet><br>
<%
tme = request("startdate"

tme = mid(tme,len(tme)-4,5)
%>
<font style="size: x-small">Time: </font><input type=text name=thetime value=<%=tme%> style="width: 50px"><input type=button onclick="seeDate();" value=" OK ">
</center>