Go to Message Wall greeting:RainbowBubbles3. There's a variety of different greetings about that look nice. My favourite, extremely simple one is Mira Laime's. You can always customise the colour, thickness of the border and font. Obviously you'll need to change the text but here is the main (slightly edited) code:
<div style="text-align: center; border: 4px solid SteelBlue; -moz-border-radius: 10px; -webkit-border-radius: 10px; border-radius: 10px; padding: 8px; width: 90%; margin: 4%">
<div style="font: bold 250% Trajan Pro, Georgia, Times New Roman; padding: 3px 3px 10px; color: SteelBlue">Welcome!</div>
Hi, I'm a user on Community Central. Please do not respond to any unanswered messages on my wall! Thanks!