Sharing Drives causes excessive WWW risk?

I have a home LAN. 4 PCs connected to WWW full time via firewalled cable modem. Each PC has XP SP2 and virus scan and its own firewall (Kerio).

I want to back up all 4 PCs to one big external HD that is run off of the main PC.. I would use the XP provided Backup utility for this from the main PC and scheduling routine backups.

For the Backup utility to work and see files on all PCs, I need to set the entire drive in each PC to "Share"..including the root.

Does this leave me more vulnerable to WWW mischief or is it not enough more to worry about.

thanks!

I do not believe that this will cause a threat from the internet. If all your computers are patched and up to date running firewalls. Cable modems are different from dial up in that it used to be a threat with sharing folders, but if you have properly configured firewalls, you should be fine. I know that cable ISPs used to recommend disabling shared files/printers, not sure if that is the case anymore. I say you would be ok, just make sure that every patch is up-to-date and you have you firewalls configured properly. I think the majority of your threat would come from your fellow cable ISP users, not the internet. I would also recommend that your turn it on only when you need to make your backups. That is my belief.
If I am wrong, please someone correct me.

what I might think about using is the built in share in windows xp. The C$ share. It is always there and should be accessible with the windows XP admin passwords. One thing I can't stress enough is if you plan on doing this make sure you are using a STRONG password. Make sure the admin account is not the main account you use and MAKE sure that you change the admin passwords. Change them frequently too. For strong password ideas use the search function on this site there are a lot of ideas.

You didnt mention if they were XP home or Pro installs. If they are home you HAVE to boot in safe mode (press f8 while it restarts and choose safe mode) then change the Admin account. This is one of the only ways to get into the admin account.

Is there any reason you are backing up the entire c: drive? why not make an image of each machine and then backup only the My Documents folder? Then you only have to share that one folder. Save everything there or to the Big hard drive.

..Don't store your data in root of drive.

If you use a tool similar to the one from http://www.karenware.com/powertools/powertools.asp you Will only need to share what you need.. not the whole shooting match

and these tools are free..

Also regardles as to how protected you are NEVER NEVER Share Root...

Often your biggest threat will start from the insde of your network..