how do i withhold txt id

You don't. Not directly & without involving some service provider like the one that exists for this app (SMSXtender), for example:
http://my-symbian.com/7650/applications/applications.php?fldAuto=596&faq=2

I dont think this is possible mate,

Although there is a program available that lets you change the number that the recipient thinks its from! (and therefore the name in the phonebook i suppose?) How cool is that,or how much trouble could you cause (depending on the user Lol),i cant remember what its called now but i know you have to buy the texts in a bundle for it,it doesnt come on your bill or credit!

😃

EDIT: Lol, N/A provided the name just as i was typing this post!!!!

It was possible with the old phones, I used to prank my friends texting with my old 7110 and 6150 using some unicode stuffs and a cable where the message would appear directly as is, u wont see the "1 message received" notification but the message itself. But your number would still appear if the recipient checked but if the recipient is dumb enough he wont be able to notice and when he press the back button he will notice that the message wasnt saved in his inbox when he checks it out. There was also this trick where you can send blinking messages or a trick that would trigger the phones alert but there would be no message, but like i said only for the old nokia phones... :frown:

And like N/A said theres no way around this but through your operators provided service or a third party app/service that has the equipments for these.