Wordpress Custom Search Filter - wordpress

Question

I've can't seem to find a solution to this so I'm posting here.
Basically I'm trying to build a basic filter for property listings. All the property listings are just posts with custom fields. For example, one of the properties has these values in the custom fields:
custom field value
------------ -----
area 150
rooms 4
bathrooms 2
garage 1
alfresco 1
study 1
theatre 1
My search form HTML looks like this:
<form method="get" id="advanced_search" action="<?php echo get_settings('home'); ?>/" >
<fieldset>
<label>Rooms
<select name="rooms">
<option value="">Any</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
<option value="5">5</option>
<option value="6">6</option>
<option value="7">7</option>
</select>
</label>
<label>Bathrooms
<select name="bathrooms">
<option value="">Any</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
</label>
<label>Garage
<select name="garage">
<option value="">Any</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
</label>
<label>Area (square metres)
<select name="garage">
<option value="">Any</option>
<option value="100">100</option>
<option value="150">150</option>
<option value="200">200</option>
<option value="250">250</option>
</select>
</label>
<label><input type="checkbox" name="theatre" value="1" /><span>Home Theatre</span></label>
<label><input type="checkbox" name="study" value="1" /><span>Study</span></label>
<label><input type="checkbox" name="alfresco" value="1" /><span>Alfresco</span></label>
<input type="submit" id="submit" value="Search" />
</fieldset>
</form>
What I am wanting to do is let the user use this filter to only show posts on a search results page that match it.
There's a slight catch too: all these custom field represents a minimum value. So if they selected "200" from "Area", "1" from "Alfresco", then it needs to show all properties that are 200 and higher and have at least 1 Alfresco area.
And - I'd like to limit the search filter to just the category called "properties".
Not asking much? :-P
Any help would be appreciated.