I've seen the traffic statistics on those "hex to dec" converter websites... I am amazed.
Many people don't know that they have a base converter right on their PC (with Windows).
You must open the ol' calculator and use the Programmer view.
Here you may see the normal, unaltered Calculator.
Click the "View" menu and select the "Programmer" item.
And this is your programmer calculator.
To convert a number, simply select the base of the current number, type it and then select the target base.
You can also do calculations in all the bases there.
I also recommend turning on the "Digit grouping" option and the "History" option (when available). You must also explore the other options (below Digit grouping).
This has been written with Windows 7... Vista should have the same features. Older versions don't...