What I used:
Rimmel white polish
Sinful Colours in Gogo Girl Red (got this in New York, its practically the same as O.P.I)
Nail Star Nail Pen in red (can buy a large range of these pens on eBay)
Nail Star Nail Pen in black
All you need to do is paint your nails red, leaving one which you paint white. Then when your white has dried, write out your valentines message. You will need a steady hand for this, keep the text short and sweet so you can fit it all in. Ask a friend for help if you find it tricky to write on your own hands.
Let me know how you get on with it, and if you get any nice surprises for Valentines day.