Did your scanner come with a software disc? Basic scan-to-text software is often given away with the scanner.
Google gives away an oldie but goodie: http://code.google.com/p/tesseract-ocr/
Or you could just search for OCR (Optical Character Recognition) software. If you want to learn more about it then your head can stand, volunteer as a proofreader for Project Gutenberg. They scan and OCR, then go through rounds of proofing and formatting to do a complete conversion to text.