Network attached storage... hooked up to an eMac?

Just a quick thought here, guys, but I'm wondering if I can plug in an external drive to my eMac and access it over the network to us as NAS without having to buy a router that will let me plug it in. I assume I can, I just don't know how to go about doing it. I could easily google it, but if you guys want to save me some time while I'm cleaning in preparation for my fiancee's parents' arrival tomorrow, feel free to let me know how to do it! eMac is running Leopard, macbook is running Snow Leopard.

Well, I googled and can't find anything... anyone want to help?

let me make sure I follow what you want...

You don't have a physical network, so no routers or switches, and you need a network accessible NAS? What do you have for a current environment?

No, I do have a network. I just don't have a drive that I can attach to it physically, and the drive isn't wireless enabled. I have my MacBook and an eMac in a network for the apartment. I can access the eMac over our network. I want to be able to attach my 500GB MyBook (WD) via one of the USB ports and be able to drop data on it from my MacBook over the network.

So something like this
$55 Addonics NAS Adapter Turns USB Hard Drive to NAS

never used it though