Create signature with Adobe Illustrator CS5

Project goal is to take a scanned (either color or? black & white) signature in JPG format and convert it to a signature with a "transparent" background using? **Adobe Illustrator** **CS5**. This signature can then be used to sign PDF documents without the need to print them. Currently using? ****Adobe Acrobat 9 Standard****. I have no prior experience with? **Adobe Illustrator** **CS5** so step-by-step instructions would be needed, preferrably with screen shots. The desired end product should result in being able to place the signature in a PDF document either via the Sign function or through the "Stamps" function under "Comments & Markup" in **Adobe Acrobat 9 Standard**. After doing some google searches I have tried several suggestions. After saving the "vector" file in GIF, EPS, etc., a white box still appeared when inserting the signature in the PDF document. So, please test with the two specific programs mentioned above. Thank you.