simple currency converter?

[Pouncer]

I'm trying to write a web service function in C# to be able to convert currencies between gbp,eur,usd

so if i called CurrencyConversion(gbp, usd, 10.00) it should convert 10 pounds into us dollars and return that, can someone give me an example how this could be done?

public class TestService : WebService
{
    [WebMethod(Description = "GBP<->EUR<->USD currency conversion", EnableSession = false)]
    public int CurrencyConversion(string currency1, string currency2, decimal amount)
    {

    }

}