Make sure all computers have the same workgroup name
Disable “Simple File Sharing” Control panel > Folder Options (This is for XP and Vista only)
Do this on all machines you want to share files from.
From here share the files you want for now just use “everybody” as far as permissions. Also adjust permissions as needed for “Everyone” (Full Control, Change, Read)
Note about users and permissions: I’m not a big fan about using “Everyone” this means that anyone on your LAN can gain access to the shares they would still need your workgroup but that is easy enough. Sounds like this is for home use so no big deal.