Yes, it is possible. It looks like your html is incorrect.
Try this instead:
Code:
<form name='whois_search' method='POST' action="/whois.php" style="margin-bottom: 0px;">
<input type='hidden' name='page' value='WhoisSearch'>
<table width="100%" border="0" cellspacing="0" cellpadding="0">
<tr>
<td height="20" colspan="3" class="darkgray">Check the avilability of your domain </td>
</tr>
<tr>
<td width="25%" height="20"><div align="center" class="darkgray">www.</div></td>
<td width="35%" height="20"><input name="domain" type="text" class="grey" size="12"></td>
<td width="40%" height="20"><div align="center">
<select name="ext0" class="grey">
<option value="com">.com</option>
<option value="net">.net</option>
<option value="org">.org</option>
<option value="biz">.biz</option>
</select>
</div></td>
</tr>
<tr>
<td colspan="3">
<div align="right">
<input name="Submit2" id='Submit' type="submit" class="formfield" value="search">
</div></td>
</tr>
</table>
** NOTE how I specified the value for each option and how that value is the TLD without the first dot, so com instead of .com, net instead of .net, etc...