Bill, if the tapes were made before 1970, then they should fine. If after 1970, the ones that held up well are BASF and Maxell. All the other brands like Ampex, etc. are prong to sticky shed syndrome. That is when the formula starts breaking down on the surface of the tape. The symptoms could be distortion, squealing and a residue left on the tape heads. If they have these symptoms, purchase a food dehydrator from Walmart like this one:
http://www.walmart.com/ip/Ronco-Five-Tr ... escriptionTransfer the tape o tapes to be processed on to metal reels. Put them in the food dehydrator set at 130 degrees for approximately three hours. When you take them out let them cool for three hours. They should play like new for at least 30 days. I would ventilate the smell from the food processor to the outside. This process can be repeated after 30 days.
You can plug you tape recorder line outs into you computer which should be able to covert analog to a digital format like mp3. You can download free software like Audacity for you recording on your computer.
Here is more info on sticky shed syndrome:
http://audio-restoration.com/baking.php This article suggests using an electric oven. I would use the dehydrator instead because you cook food in the oven.