This may be a simple question, but how does one calculate the melting point of ice at a given pressure when density of ice and water are given and the heat of melting? I also have pressure and temperature of the tripelpoint of water.

I suggest instead of looking for a simplified a possibly inaccurate formula, tray googling for say "melting curve water" (or "...ice"). The curve at answers.com or at Martin Chaplin's site should work for you.