Da me funziona benissimo con IE 6.0 !!!
Comunque se non usi IE prova cosi....

codice:
<DIV ID="pluto" STYLE="position:absolute;top:200;lest:40;">   
<FORM>
<input type="checkbox" name="c1" onClick="show_hide(T1)"><INPUT TYPE="text" NAME="T1" SIZE="20">


<input type="checkbox" name="c2" onClick="show_hide(T2)"><INPUT TYPE="text" NAME="T2" SIZE="20">
</FORM>
</DIV>