As a side-note, you might want to check for firmware updates for your Linksys WCG200. I'm aware of at least one Linksys model that struggles as described HERE (click link). But I haven't heard of this issue for other linksys models.

When you say wireless, is the receiver a card within your computer? Is there any usb or ethernet cabling between any of the devices?

It's not comcast. I have comcast and they allow p2p.

This is not true. Read the terms of service before you claim
anything:

http://www.comcast.net/terms/use.jsp

"Prohibited Uses and Activities Prohibited uses include, but
are not limited to, using the Service, Customer Equipment,
or the Comcast Equipment to:
[...]
14. run programs, equipment, or servers from the
Premises that provide network content or any other services
to anyone outside of your Premises LAN (Local Area Network),
also commonly referred to as public services or servers.
Examples of prohibited services and servers include, but are
not limited to, e-mail, Web hosting, file sharing, and proxy
services and servers;"