My modem is in an upstairs bedroom. The cable is fed through the outside wall of the house into this room. My cable company did that. I've got a new computer downstairs, almost directly underneath the modem, (probably about 10 feet to the right and then underneath) that I'd like to get an ethernet cable to for a LAN internet connection. (Wireless is less reliable and has been causing weird sounds in my cordless phones. I'd rather do LAN.) What would be the best way to do this? Feeding the wire down the stairs would look kind of sloppy and waste a lot of cable. Could I feed it through the outside of my house from the upstairs and then back in through the downstairs? (I live in a place that gets snow and rain.) Or could I hook up an ethernet jack downstairs and feed cabling through my walls somehow? What supplies would I need and what would be the best method?

go as close to a corner of the room you can then drill a hole thru the floor to the room downstairs.

The fastest way may be going outside and down the wall and back in. For protection you may run either an exterior grade cable or use conduit. I have run ordinary interior cable out a window and back in another window. It's been running for 3 years, but only exposed to rain and not cold. Drilling a hole and dropping in a wall or floor is probably the best. Avoid exterior walls, it may be difficult to go through insulation.

My house had the basement fully finished when we bought it. Whoever did the basement did a very nice job with one exception. They used drywall on the ceiling so I can't pull any phone/data/electrical in this house without first destroying the ceiling in the basement *sigh* Once my wife got her promotion and started working from home we set her up a home office in one of the unused bedrooms upstairs. I have my office in the basement on the south side of the house. Her office is on the north side but at the same end of the house (west). So, to provide her with a cable (wired access is so much more reliable) I drilled a hole through the ceiling of my office in the closet. This matched up with the closet in the bedroom above my office. I then drilled one hole through the wall of that closet and into her office. All in all, while it's not what I would have done had my basement ceiling not been drywalled (ie: outlet boxes, faceplates and keystones wired to a patch panel in my office) it works and it's neat, tidy and you can't see the cable unless you go into the closet in my office. I wouldn't recommend going outside if you can avoid it. If you own the house and the basement ceiling is a drop ceiling, you could do a neat, tidy job by drilling up through the bottom of the wall from below and using a fishtape to pull the cable up from downstairs. Make a hole the exact dimensions of an outlet box and buy a plastic insert type unit that will hold a faceplate and use that. Then all you'd need is a faceplate and a keystone or two.