I've always wanted to do that, by any minimal chance you wanted to know how I did that:
1. Selected Picture in Microsoft Paint with select tool.
2. Copied and pasted it to Microsoft Word.
3. Selected the picture, and clicked the button, "Grayscale".
4. Copied and pasted it back into Microsoft Paint.
That's how I did it.
And yes, some people *coughZashtheHedgehogcough* were wondering, yes that background is from Nuclear Dimes.
Now Microsoft owes me for advertising!