I have recently purchased this program and finally can get 3 pics into one banner......but when i try to type in a text it either tells me my clipboard is to full or i need to flatten the image and i do this and it still won't work and some other message comes up when i try it........could someone help??????

What does the other message say??
And maybe you have to merge flatten it..are you doing that or another flatten?

To add a text go to Layers >> New Raster Layer. And why can't you merge the image? What does it say?