You can have two scanners with the same resolution, but that will produce different quality images. Why? Because they have different bit depth (also known as pixel depth).
Whether the scanner is 1200x1200 or 4800x4800, bit depth is critical. The smaller the bit depth, the less information will be contained in the file. Bit depth is a bit complicated to explain; suffice it to say that it means that the scanner can offer more color information in each pixel, resulting in more accurate colors. Look for the highest bit depth you can get -- but be aware that PCs can't handle more than 24 bits. (Some scanners may say that they have a 48-bit internal depth, but this is technical slight-of-hand. The important part is the external depth, and that is actually 24-bit.)
ARCHIVING
You will have the choice of saving your file in one of several file formats. Most professional photographers use TIFF (.TIF) formats for their final versions, and JPEG (.JPG) for images that they are going to store for reference. The TIFF format does not compress the data, which means that none of the information in the file has been eliminated to save space -- and which means that the image will not have that "dotty" look that you see in newspaper photos.
However, the TIFF format also creates large files. If you want to save a bunch of images on your hard drive, or use a simple photo editing program (rather than a higher-end one such as Photoshop), you may want to save the TIFF master images in JPEG format. JPEG will compress your images so that they will take considerably less space, and do it very efficiently, and with as little effect on the image quality as possible. However, there may be some loss of quality. (See article on file formats).
