Well I don't know what version of Windows you have. I have WinXP and calc.exe only performs binary conversion for integer numbers (char, short, int)... NOT for single and double precision IEEE 754 numbers. That's why I think this website provides more features than the traditionnal Windows calc.
Here is a good tool for checking your solution when converting a number from decimal to binary or from binary to decimal.
It supports integer numbers (8, 16 and 32 bits) for both unsigned and signed numbers.
It also includes a converter for single precision and double precision numbers...