What you’re talking about is called a Wireless Access Point, and they do exist. Here is a link to an explanation of them:

http://en.wikipedia.org/wiki/Wireless_access_point

You could also use a Range Extender, also called a repeater. These you place within range of your router, they connect to the router wirelessly, and accepts wireless connections coming in, and then act as a relay. You can read more about these here:

http://compnetworking.about.com/od/wireless/ss/wirelessgear_7.htm
http://compnetworking.about.com/b/a/229360.htm

Still yet another solution is to use a signal booster on your router. These are not as common but I have had better experience with them. The one I have used the most and found to be the best is the Hawking [HSB2] Hi-Gain WiFi Signal Booster.

http://www.hawkingtech.com/products/productlist.php?CatID=32&FamID=72&ProdID=187

Another option would to replace the antenna(s) on your router with high gain antenna(s), if the router has replaceable antennas on it. I have tried several brands of antennas and again found the ones from Hawking to be the best in their price range. Most of these will also work on your wireless network adapter if it has a replaceable antenna on it, most PCMCIA/PC Card wireless adapters do not. The wireless cards that plug into a PCI slot for a desktop computer generally have removable antenna, and some but very few USB wireless adapters have a replaceable antenna. Here is a link to Hawking’s high gain antennas:

http://www.hawkingtech.com/products/index.php?CatID=32&FamID=58

Hawking also has a few USB wireless adapters with a built in high gain antenna, I have also had good luck with this one:

http://www.hawkingtech.com/products/productlist.php?CatID=32&FamID=60&ProdID=280

If there was it would cost as much as an ethernet card with a wireless built in.

Never seen what you are looking for though. interesting idea though.

Think of the wireless router as a light source, like a lamp.. try to position it as high as possible and try to not have any heavy objects like a fridge or the central AC unit in a direct path between your computer and the router. In the router it might have an antenna power level, you might be able to boost it.

Most wireless routers can connect like 150 feet without an issue, you can pick up your neighbors routers from a few houses away in some places.

Yes, it’s called an Ethernet Bridge. You can plug it into the Ethernet cable that goes to your room and either plug directly into the computer, or a switch (so you can have more than one computer up in that room, all connected through the Ethernet cable to the Bridge). Linksys makes one called the WET54G. Dlink has a couple of items that would work. One is the DWL-G730AP. it’s actually an Access Point / Ethernet Bridge combo unit. It can be set to operate in either mode. (When it is a Bridge, or "client", it will connect your ethernet network – or PC – to a Wireless network, and when it is an Access Point, it will "create" a wireless network from an Ethernet network – Great for traveling with a laptop if all the hotel has is Ethernet and you want wireless.) Dlink also has the DWL-G820 (Which is designed for hooking your game console – eg. Xbox or Play Station – to your Wireless Network) that would do virtually the same job as the Linksys WET54G.

As far as your wireless signal goes.. What model specifically is it? Most wireless routers will get several hundred feet of range, depending on environment. So for example, if you are just in the room across the hallway, or upstairs, there would be no problem connecting. However, if you have a farily large house and the Router is on one side, and you are trying to connect to it from the other side, you may get a signal, but it may be spotty or too weak to connect to. The biggest factor is how many walls does it have to go through, and what are they made of? (Sheetrock isn’t as difficult for Wireless radio waves to pass through as Brick or concrete) Typically in an average home, if the Router is placed relatively center to the home, just about every room can see it and connect without much of a problem. Whereas, if the Router is placed on one side or the other, the far rooms can sometimes get a signal, but they will have a much harder time connecting well, if they connect at all.