How to convert the meters to degrees in GCS_WGS_1984?

Hi Everybody:

I am writing ArcObjects tool that works on the data with WGS84 spatial reference, where the X/Y coordinates are degrees. I want to use ArcObjects to buffer a point with 1 meter distance. If I use the ITopologicalOperator.Buffer, it will buffer the point with a number in the unit of degrees. I don't know how to get this number now. Do you have any idea?

Here is what I know at this moment:
* if I the point's spatial reference is an IGeographicCoordinateSystem but now a IProjectedCoordinateSystem
* the IGeographicCoordinateSystem.CoordinateUnit.ConversionFactor and IGeographicCoordinateSystem.CoordinateUnit.RadiansPerUnit are both 0.017453, which is roughly PI/180, which is not telling how many meters each degree is
* I am using ArcObjects 10.0

Any idea? Thank you!