xp pro, 3 home comp. want to share all safely

have 3 home comp. networked with xp pro and linksys switch EZXS55W and each comp. has phone line to it for dial-up (modum and home network). would like to somewhat safely share everything on the home computers (dial-up, printer, even C: drives) but not be vulnerable when on-line with dial-up. use to use netbutal with ME and two comp. and was pretty happy with set up and the password system. I have read about networking XP and realize this is a lot harder task. I have tried some diffent things like removing simple file sharing but have no real idea if I'm protected, probably not. Want to share dial up so we can be online at same time but also like to use phone line on each computer if main comp. off. Have to share printer. I also get real tiried of reading call your netwok administator!!! I guess that's me!!!! Wouldn't even mind if I could only home network when off line from dial-up with the exception of sharing the dial-up connection. Currently I don't have the Bios system administator password protected. I also don't totally understand the firewall system, can I set up the firewall to close sharing and home networking with the excecption of sharing dial-up when dial up conection present!!! Any help greatly appreciated.