Hi

  I have a idea in  my mind...

     I will write code for text field in a panel . panel will be hidden defaults.. when other valu is choosen from picklist then outputpanel is rendred.

<apex:page controller="Mycontrollernew">
<script type="text/javascript">
function Callmefunc(id)
{
alert(''+id);
var type = document.getElementById(id).value;
alert(type);
alert('hi');

check(type);
return true;


}
</script>
<apex:form>
<apex:pageBlock>
<apex:pageBlockSection>
<apex:inputField value="{!account.Type}" id="check" onchange="Callmefunc('{!$Component.check}');">
<apex:actionFunction name="check" action="{!makingfield}" reRender="refresh">
<apex:param name="Mahavir" value="" />
</apex:actionFunction >
</apex:inputField>
<apex:outputPanel rendered="{!readonly}">

<apex:outputLabel value="Entry" for="tst">
<apex:inputText id="tst"/>
</apex:outputLabel>

</apex:outputPanel>
</apex:pageBlockSection>
</apex:pageBlock>
</apex:form>
</apex:page>

And My controller is 

public class Mycontrollernew {
public Account account{get;set;}
public String act{get;set;}
public Boolean readonly {get;set;}
public Mycontrollernew(){
}

public void makingfield() {
act =System.currentPageReference().getParameters().get('Mahavir');
System.debug('!!!!!!!!!!!!!!!!!!!asish!!!!!!!!!!!!!LeadType!!!!!!!!!!!!!!!!!'+act);
if(act=='Other') {
readonly = true;
}
}

}

You need to care about Renrded about.

Did this post solve your doubt if so please mark it solved.

Thanks

asish