New wireless laptop Pentium M running Windows Media Center;  three year old Pentium 4 desktop running Windows XP Service Pack 2.  Linksys Wireless-G Router.  I have read through previous postings and most are beyond my expertise.  I have successfully connected to the internet (highspeed cable connection) with both computers.  I have run the network wizard and have named the network on both computers.  I have disabled Windows Firewall on both computers.  I have read everything I can find and tried everything suggested.  Problems:  1) I have been unable to share files although I have marked several files for sharing.  2) I have been unable to access the printer (from the laptop) which is plugged into the desktop .  3) I can access the internet from the laptop through Internet Explorer but not through Firefox.  4) I cannot access ITunes music store from the laptop.  5) I cannot connect to America OnLine from the laptop.  I have called both Linksys and Dell and neither will help.  Dell referred me to a paid service which I have not subscribed to.  Any suggestions will be greatly appreciated.