...
<form action="foo" method="post">
	<fieldset>
		<legend>Pers&ouml;nliche Daten</legend>
		
		<!-- Start Anrede / Radiobuttons -->
		<fieldset class="radio_btn">
			<legend>Anrede: </legend>
				<input type="radio" id="herr" name="anrede" value="herr" checked="checked" />
				<label for="herr"> Herr </label>
				<input type="radio" id="frau" name="anrede" value="frau" />
				<label for="frau"> Frau </label>
		</fieldset>
		
		<!-- Start Daten / Auswahl verschiedenster Elemente -->
		<fieldset class="daten">
			<legend>Daten-gemischt: </legend>
				<label for="namen" class="left" >Namen etc.:</label>
				<input type="text" id="namen" name="namen" class="formtext" /><br />
				<label for="strasse" class="left" >Stra&szlig;e: </label>
				<input type="text" id="strasse" name="strasse" class="formtext"/>
				<label for="strNr">Nr.: </label>
				<input type="text" id="strNr" name="strNr" /><br />
				<label for="plz" class="left" >Plz.: </label>
				<input type="text" id="plz" name="plz" class="plz"/>
				<label for="ort">Ort: </label>
				<input type="text" id="ort" name="ort" /><br />
				<label for="telefon" class="left" >Telefon: </label>
				<input type="text" id="telefon" name="vorwahl" class="formtext"/> - 
				<input type="text" name="durchwahl" /><br />
			
				<label for="land" class="left" >Land: </label>
				<select name="land" id="land" class="formtext">
					<option value="">-- bitte w&auml;hlen --</option>
					<option value="DE">Deutschland</option>
					<option value="AU">&Ouml;sterreich</option>
					<option value="SU">Schweiz</option>
				</select><br />
			
			<label for="email" class="left" >E-Mail*: </label>
			<input type="text" id="email" name="email" class="formtext"/>	
		</fieldset>
		<input type="submit" value="absenden" />
	</fieldset>
</form>
...

body {
	font-size: x-small;
	font-family: Arial, Helvetica, sans-serif;
	}
	
.left {
	width: 13em;
	float: left;
	display: block;
	}

.formtext {
	margin: 2px 2px;
	padding: 3px 3px;
	width: 14em;
	}

.plz {
	margin: 2px 2px;
	padding: 3px 3px;
	width: 5em;
	}

<div>
  <input type="text" style="width:100%" value="Straße" /></div>
<div>
  <div style="width:75%;float:left;margin:0;padding:0"><input type="text" style="width:100%" value="PLZ" /></div>
  <div style="width:24%;float:right;margin:0;padding:0"><input type="text" style="width:100%" value="Stadt" /></div>
  <br style="clear:both" />
</div>