The most likely reason you cannot share is due to the Linksys. By default the Linksys acts as DHCP server to the hosts (PCs/MACS etc.) connected to the 'private' side. This will ususally assign IP addresses such in the 192.168.1.x class. Several IP ranges do not route (by design) on the internet..... 192.x.x.x being one of them. The internet side of the Linksys acts as a host using the IP assigned to you by your ISP.... but it masks your inside PCs in terms of that IP address so the folks trying to share from you are seeing the 192.168.1.x address and are prevented from communicating with you since they cannot establish communication using that IP range. You can configure the Linksys to make one of you... by assigning one PC's IP (the one you want to use as a shared PC) to be in the DMZ (a configuration that will allow the internet to establish communications with you PC) -

Get your Linksys manual out -- here are the general steps

- Log into the router
- Http://192.168.1.1
- Use the user name and password as refererred to in the owners manual
- Click on the ADVANCED tab
- Click on DMZ host
- Enter the IP address used by the PC you want to be exposed At that point the IP selected should be 'visible' to the world