<<< The second acomputer can access the printer functions of an all in one Photo printer but not the scanner >>>
Windows "File & Printer Sharing" only supports printing over the network, it doesn't support the remote use of scanners.
<<< It cannot access shared files on the main computer. >>>
Which version of Windows is the "main" PC running. XP Professional is more problematical than Home Edition. You may have to be logged into both PCs with an identical Username/Password. Have a look at this page - click here