You can buy a programe called "Hallnark Card Studio" and while the cards are probibly copyright you can start with a blank and add your own verse etc. I baught one years ago and find it very easy to use.
If I want to type the greeting on before printing I import the sheet into Photoshop elements then use the add text tool. Having decided on font, size & colour I tell it to centre. Once typed I can use the move tool to position it if I dont like where it is. I have just done one the the Sandie Burchell popout ones where I put the greeting onto the back of the card first & picked out the colour for the text from one of the flowers. If you need a hand Carol send me an email & Ill pop over sometime x