home network security

I need to know how much risk is involved in sharing my internet connection with my flatmates.

I have broadband and a wireless router with a WEP encrypted network that I share with my three
flatmates.

On my machine I have a firewall and Kaspersky internet security etc. (running Windows XP pro SP3) But is it possible for a virus or trojan
on another computer on the network to launch and infect files for example if I am updating my zen cart or
using FTP to one of my virtual hosts? Can another machine on the network send malicious files via a connection I
have initiated on my computer?

Thanks :-)

As far as it relates to your Zen Cart site, don't use just regular FTP. Use SFTP so your communications is encrypted, thus preventing anyone else on your internet connection from doing anything rogue with your activity.

As far as viruses and one computer affecting another computer, that's outside the scope of Zen Cart.

So what about normal admin stuff I do via a browser (which is how most of the zen cart changes, additions etc. are done)? Do the other computers on my network pose a potential danger if they were to have some type of malware?

Other computers on your local network are only a "risk" if they're sniffing all the traffic on your internet connection and watching everything that goes by.
If they're doing that, then they're reading all your email and watching every page you surf -- basically everything you do online that's not encrypted with SSL.

So, yes, if you're paranoid about these flatmates and their computing practices, or just concerned about protecting traffic to/from your admin area from prying eyes, then set up your admin configure.php file to use SSL for all admin activity.
That won't stop others from snooping around, but will stop them from seeing the data sent back and forth between your browser and those secured pages.

trillian:

I
I have broadband and a wireless router with a WEP encrypted network that I share with my three
flatmates.

Don't use WEP.. it can generally be cracked within 30-60 seconds.

Cheers
Rod