Checking Domain name availability (DNS tools?)

I need to have a field on one of the pages on our site check domain names for availability. We are a reseller of stuff like that, so I have access to whatever APIs our provider offers, but I don't have to use theirs only, I can use something like the http://domaintools.com stuff.

My question is, what is involved in getting this to function, from step 0? (Step zero is having a configured zencart but not much past that)

Thanks in advance, get as technical as you'd like.

-Tim

This has been solved as well, I used Sam's WHOIS for the basic function and modified the code slightly to get it to work in my environment.

<script src="/whois/samswhois/populate.js"></script>
<form id="whoisform" name="whoisform" style="margin: 0px;" action="#"  method="get">
<div class="swForm">
<input type="hidden" name="main_page" value="index" />
<input type="hidden" name="cPath" value="12_81" />
<div class="swHeading">Whois Lookup</div>
<input type="text" name="domain" id="domain" class="swDomain" value="domain" onFocus="this.select();" />
<b>.</b> <select class="swtld" id="tld" name="tld"><option value="com" SELECTED >com</option>
<option value="net">net</option>

<option value="org">org</option>
<option value="info">info</option>
<option value="biz">biz</option>
<option value="us">us</option>

<option value="co.uk">co.uk</option>
<option value="org.uk">org.uk</option>
<option value="ltd.uk">ltd.uk</option>
<option value="ca">ca</option>

<option value="cc">cc</option>
<option value="edu">edu</option>
<option value="com.au">com.au</option>
<option value="net.au">net.au</option>
<option value="de">de</option>

<option value="ws">ws</option>
<option value="sc">sc</option>
<option value="mobi">mobi</option>

<option value="pro">pro</option>
</select><input type="button" onClick="populate();" name="lookup" value="Search!" class="swSubmit" />

</div>
</form>
<!-- 
	a little bit of javascript that sets the keyboard focus to either the domain field,
	or the security code field if the user has just submitted the form without entering
	the correct value.
-->
<script language="JavaScript" type="text/javascript">
<!--
document.forms['whoisform'].domain.focus();
//-->
</script>

I hope this helps someone like myself save a bit of time.

-Tim