First, check the images that you already have. Right-click on the thumbnail (in the folder/album view), and check to see what the actual size of the image is. If the size is larger, then you just haven't opened the file. If the images have been reduced to a thumbnail size, then you may have to reset the settings for the scanner.
If the thumbnails are just the preview, then select the file, and open it with your editing progam (photo-shop, ms paint, jasc, etc.)
If the files have been resized, check the settting for your scanner, to make sure that it scans images to the size you want. There may be default settings(drop down menu), or you may be able to customize them (fill in boxes).
Otherwise, you will need to check the scanner manufacturer's website for patches (to make your scanner more compatible with your OS, for example if you scanner is rated for Win ME, and you are now using XP) or hotfixes. Also check their site for troubleshooting and faq, to see if they have help for this problem.
Finally, if you still cannot scan and save the files to the desired size, you might want to uninstall the scanner software, reinstall the scanner, and re-execute the startup tests.