Canon PowerShot S51S camera, trying to transfer photos from computer onto the memory card so we can use the card in a digital photo frame? Don't know how to transfer?

Try sending the photos to a cloud service on the web, then transfer to a memory card that could be inserted into the Photo Frame. If the phone has a memory card you can get an adapter to upload to a PC then back to a memory card for the Photo Frame.

The best way to download pictures from your camera to your computer involves removing the memory card from the camera and plugging it into a card reader (either built-in to the computer or connected via USB or FireWire). This is likely to be faster than connecting the camera to the computer, and won't run down your camera's batteries.

Once the card is plugged in, it will appear to your computer as a removable drive. You can use the operating system's drag&drop facility to copy pictures from the card to the computer's hard drive, the same way you copy any other files. Or you can use any photo management program such as Picasa ( http://picasa.google.com ).

ALTERNATE WAY TO TRANSFER PHOTOS AND VIDEOS TO A COMPUTER
If your photos and videos are stored on the memory card, then remove the memory card from the camera and insert it into an USB memory card reader. Connect this USB memory card reader and memory card into the USB port of your working computer. Your computer will see this as an USB Mass Storage Device or an external storage device; you can then open the folder on the memory card and copy the photos and to your computer. Memory card reader is a handy device and is inexpensive. You can copy photos from other cameras and you can also download photos off your memory card to someone else's computer without the need of installing any programs.

ALTERNATE WAY TO TRANSFER PHOTOS TO COMPUTER
If your photos are stored on the memory card, then remove the memory card from the camera and insert it into an USB memory card reader. Connect this USB memory card reader and memory card into the USB port of your working computer. Your computer will see this as an USB Mass Storage Device or an external storage device; you can then open the folder on the memory card and copy the photos to your computer. Memory card reader is a handy device and is inexpensive. You can copy photos from other cameras and you can also download photos off your memory card to someone else's computer without the need of installing any programs.

From page 156 of the "Advanced Camera User Guide":

The file name could not be created because there is an image with the same name as the folder that the camera is attempting to create, or the highest possible file number has already been reached. In the Set up menu, set [File Numbering] to [Auto Reset]; alternatively, save all the images you with to retain onto a computer, then reformat the memory card. Please note that formatting will erase all the existing images and other data.

Try opening the windows XP default picture wizard to transfer the pictures or use a memory card reader to transfer if you have one.

Please don't take this as a sales pitch as it's not, but please see the following blog article, as it describes the use of an inexpensive card reader as a much easier, faster, and less error prone way to download your photos AND videos. In fact there are several important reasons discussed in the article for using a card reader vice downloading from the camera. USB Card readers are also very inexpensive these day, with cost virtually not an issue:
http://camerarepair.blogspot.com/2009/01/how-do-i-download-photos-or-pictures.html

TURN CAMERA ON FIRST, PLUG IN USB, GO TO MY COMPUTER, YOU WILL SEE A DRIVE THAT HAS YOUR CAMERA ON IT. YOU SHOULD BE ABLE TO DOUBLE CLICK AND OPEN THAT DRIVE.

ANOTHER THING YOU CAN DO IS TAKE MEMORY CARD OUT OF CAMERA, PUT MEM CARD IN COMPUTER, GO TO MY COMPUTER, FIND DRIVE WITH MEMORY CARD. DOUBLE CLICK AND OPEN FILE.

YOU CAN CLICK AND DRAG PHOTOS FROM THAT DRIVE AND DROP THEM IN ANY FOLDER OF YOUR CHOICE.

YOU MUST HAVE THE LATEST USB DRIVERS FOR YOUR EXACT CAMERA FOR YOUR COMPUTER TO READ IT.

Although you can copy images from your computer to your camera, the camera will be unable to display them, so it is a pointless exercise.

Your camera is designed to be a source of pictures, not a destination. If you want to copy pictures to a memory card, you need to use a card reader and not a camera.