This can probably be tweaked to suit your needs:

// from
// http://www.devcity.net/forums/topic.asp?tid=7267
public static bool isNumeric(object val)
{
try
{
//string val = value.ToString();
double d = System.Double.Parse(val.ToString(),
System.Globalization.NumberStyles.Any);
return true;
}
catch (System.Exception)
{
return false;
}
}