well, doing the graphics would be differnt, but here the general idea for getting the input (because the input command wouldnt be of use in this)
when the textbox is selected, have it read what keys are being pressed, so if they press 'A', it adds 'a' to the string. so string VAR = "a", then when they press the letter 'N', it will add that to the string, so string VAR = "an", if they get a BACKSPACE key, it will remove one, so string VAR = "a".
so, in a little more codish looking way :p
blah as string
key as string
`main loop
do
key = inkey$()
blah = blah + key
text x,y, blah
sync
loop
you can add a:
if scancode() = 14 `backspace
block too to remove the last char
and you would have to make sure it wont let you hold down like it does now

<[jimmy]> daaaaaaaaaaaaang that KK is cute