Diagram illustration

Hello, This is possibly a simple job (but I still can't so it!) . I have designed a diagram (basically 3 overlapping coloured circles with some text). I did this using the microsoft paint software (saved as a bitmap)..so it is crude and very pixelated when it gets blown up. I would like the diagram to have roughly the same colours (like traffic lights) but with a glossy, professional look. Something that I can expand or shrink without distortion. I will typically use this diagram in documents or in powerpoint slides, plus eventually on a website. Would that mean saving it as a jpeg? Thank you.