Yes, you can. I assume that you currently have all three attached to LAN ports on the modem and/or a wireless connection.
What OS is on the computers? For example in Windows 7 you can select the drive or files that you want to share, right click on them and then make changes to the sharing AND security tabs; in the security tab the easiest thing to do is to add a share group name Everyone and then set the sharing tab to the level sharing you want.
As long as all three are on the same network (wired or wireless doesn't matter) you just right click a drive or file and select sharing and set the attributes you want. For Windows 7 you must also set the security tab by adding an Everyone share group.
Also make sure that each machine is a member of the same workgroup, and WORKGROUP should be the default unless changed.
done all computer are now available every computer's network places or in windows 7 network center..now problem i am facing is that PC with windows 7 is sharing all files but PC with windows xp didn,t.they ask for username and password first windows 7 also ask for user and password i disable it from
Control Panel>All Control Panel Items>Network and Sharing Center>Advanced sharing settings>password protected sharing