Here's an example that places a spellcheck image next to a text field and a textarea. When the user clicks the image, the fieldname is passed to doSpell() and the form field is spellchecked.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>SpellChecking a form field</title>
<script language="javascript">
function noop() {}
//called when the Check spelling button is clicked
function doSpell(fieldname) {
window.open("/spellchecker/window_jsvar_document.myForm..html" + fieldname + ".value", null, "height=230,width=450,status=no,toolbar=no,menubar=no,location=no");
}
</script>
</head>
<body>
<form name="myForm">
<input type="text" name="firstTextField" value="somtin" size="30">
<a href="javascript:noop();" onClick="doSpell('firstTextField');"><img src="/support/kb/indexcfm/fuseaction/single/id/1015/images/spell.gif" border="0"></a>
<br>
<textarea name="content" rows="14" cols="45">I am speled wrang</textarea>
<a href="javascript:noop();" onClick="doSpell('content');"><img src="/support/kb/indexcfm/fuseaction/single/id/1015/images/spell.gif" border="0"></a>
</form>
</body>
</html>