Arbitrary type of precision

In your teleobject, you have to specify numbers that are arbitrarily large, and for this question, yes, there are various Big Integer libraries available (I assume .NET 4 includes one of these in the Framework).

However, the title of the question refers to "precision", which assumes that you want to draw an arbitrary number of digits to the right of the decimal point - and for that you need either a Rational class (in conjunction with a Big Integer) if you are only dealing with rational or a smart symbolic manipulator (like Mathematica) if you're going to leave rational use.