is there some software that would take a sketch drawn by hand and scanned and then convert it to a Visio (or similar software ) chart I can edit ?
I assume your sketches are in a bitmap format such as .jpg .png or .bmp
And you want to convert this to a format where you can individually edit the components in the drawing such as lines, shapes, etc. rather than a painting tool which just works with the pixels.
vectormagic.com converts bitmaps to the open w3c approved standard, SVG, Scaleable Vector Graphics. The resultant SVG file can be edited in many tools such as the free Inkscape, Corel, Illustrator. It can be viewed in several web-browsers (plug-in may be necessary) and then converted back to bitmap if needed.
vectormagic.com provide a free online tryout service, then pay per image after that. They also offer downloadable software for a one-off fee, though more expensive, but provides unlimited conversioms.
Another benefit of having it in SVG is that the drawing can be enlarged without loss of quality, i.e. no jaggy edges.