Here some instructions:
NOTE:
Those instructions require working in CODE view mode and are for Advanced users!

1. First you need to pass the variable to the script that populates the Calendar.
You will find the script path in Scrip tag that is right after the calendar markup. Generally looking like this:

<div class="dmx_ajax_event_calendar elegant_blue" id="dmxAjaxCalendar1" style="width:700px;"></div>
<script type="text/javascript">
  // <![CDATA[
jQuery(document).ready(
   function()
     {
       jQuery("#dmxAjaxCalendar1").dmxAjaxCalendar(
{id:"dmxAjaxCalendar1", width:700, height:500, allowed_display_types:[true, true, true, true], legend_position:"bottom", display_type:3, events_type:[{number:0, name:"Australian", color:"#000099", background_color:"#FFFFFF", border_color:"#FF0000"}, {number:1, name:"Canadian", color:"#FF0000", background_color:"#FFFFFF", border_color:"#FF0000"}, {number:2, name:"China", color:"#FFFF00", background_color:"#FF0000", border_color:"#FF0000"}, {number:3, name:"German", color:"#000000", background_color:"#FF0000", border_color:"#FFFF00"}, {number:4, name:"Indian", color:"#FFFFFF", background_color:"#336600", border_color:"#FF9900"}, {number:5, name:"Russian", color:"#FFFFFF", background_color:"#0000CC", border_color:"#FF0000"}, {number:6, name:"USA", color:"#FF0000", background_color:"#FFFFFF", border_color:"#0000CC"}], google_feeds:[], ajax_feeds:[{url:"calendar_ajax/calendar_get_events1.asp"}], link_google_events:true, use_working_hours:true, working_hours_start:8, working_hours_stop:18}       );
     }
);
  // ]]>
</script>

So, you are looking for following :

ajax_feeds:[{url:"calendar_ajax/calendar_get_events1.asp"}]

2. Here you need to add your URL param like this:

 ajax_feeds:[{url:"calendar_ajax/calendar_get_events1.asp?ParamName=<%= QueryString("ParamVariable")%>"}]

Where ParamName is the name of the URL Variable that will be passed to the calendar Script and ParamVariable is the name of your current URL variable name.
3. Once this is set on your calendar page you need to open the calendar_ajax/calendar_get_events1.asp
There you need to retrieve the URL variable passed in the path on the Calendar page so change following:
3.1. On line 22 add “, request_Filter “ so the line look like :

Dim request_Start, request_Stop, request_Filter

3.2. Go to the end of line 25 and set a new line.
3.3. On the new line ( must be number 26) set following :

request_Filter = Request.QueryString("ParamName")

Go to line 46 where the SELECT statement is defined and change it ot:

dmxEventsRs_cmd.CommandText = "…[Truncated]… WHERE columnName [ = , != , LIKE] 's' AND DATEDIFF('s',#01-01-1970#,[start]) <= ? AND (DATEDIFF('s',#01-01-1970#,[stop]) >= ? OR ([stop] IS NULL AND DATEDIFF('s',#01-01-1970#,[start]) >= ?))"

3.4. Go to end of the line 46 and set new line ( number 47 ) and set there following (set one of the types 3 or 200 depending of what type is your variable ID – Integer – type 3 , text – String – type 200 ):

dmxEventsRs_cmd.Parameters.Append dmxEventsRs_cmd.CreateParameter("@filter", [3 - integer , 200 - string], 1, , request_Filter)

Well… save the files and upload them . Test and if any problems call back.