how do i set validation on select tag in my form

how do i set validation on select tag in my form

i want to set validation on select tag in my form so that the user cannot
proceed without choosing a location.
below is the form...
<form name="form1">
Pickup Suburb:
<select id="pick" class="pick" name="pick"/><br />
<option value="none">-- Please select a location --</option>
<option value = 1>City </option>
<option value = 2>Airport </option>
<option value = 3>Abbotsbury </option>
<option value = 4>Abbotsford </option>
<option value = 5>Acacia Gardens </option>
<option value = 6>Agnes Banks </option>
<option value = 7>Airds </option>
<option value = 8>Akuna Bay </option>
</select>
<br />Rear facing baby seat <select class="rfbs" name="rfbs"
style="width:50px">
<option value="0">0</option>
<option value="1">1</option>
<option value="2">2</option>
</select><br />
<br />Booster seat <select class="bs" name="bs" style="width:50px">
<option value="0">0</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<br /><br />Luggage Trailer <select class="lt" name="lt" style="width:50px">
<option value="0">0</option>
<option value="1">1</option>
</select>
<br />
<br /><input class="show-popup" type="submit" value="Get Quote">
</form>
i have applied a javascript popup window to show the results when user
fills the form so is it possilbe to apply validation that shows a
error,message if the user tries to submit the form without choosing a
location.
any help would be highly appreciated.
Thakns.