You can't use a second DSL modem without a second phone line and DSL account.
The most reliable, and cheapest way is to run the 50' Ethernet cable. Nothing to set up - Just plug the cable into the PC and Router and it will work.
If you don't want to run a cable you could use Ethernet over powerline adapters at both ends. http://www.amazon.com/Netgear-85Mbps-Powerline-Network-Adapter/dp/B001AZUTCS/ref=sr_1_3?s=electronics&ie=UTF8&qid=1304154945&sr=1-3
If you want to go wireless you will need both a wireless access point or a second router with wireless features and a wireless adapter for the second PC.
You may just want to replace your Qwest modem/router with one that has wireless features built in. http://www.amazon.com/Actiontec-GT724WGR-Universally-Compatible-Wireless/dp/B0018CJ9LA/ref=sr_1_5?s=electronics&ie=UTF8&qid=1304156759&sr=1-5
To use a wireless connection, you'll have to purchase a wireless adapter for the PC. You can either install a card in the computer or buy one that plugs into a USB port. They are fairly inexpensive.
There are two current wireless standards, the newest is wireless N (300 Mbps) and the older is wireless G (54 Mbps). Either one will work fine with your Qwest DSL Internet connection.
Being that your Qwest DSL Internet connection (WAN) is most likely 1.5 to 6 Mbps and wireless G is many times faster at 54 Mbps, there is no real advantage in Internet speed by choosing wireless N. The only advantage would be in transferring files around between computers on your local LAN. Wireless N also has a larger range, meaning you can get a wireless signal at a larger distance from the router. However, remember to get either the speed or range improvements of wireless N, both devices have to be N. A wireless N router hooked to a wireless G adapter on a PC will have the range and speed of wireless G.
I'm not saying not to buy a wireless N router, I use one myself. Just don't expect any improvement in Internet speed. People that recommend N to improve Internet speed don't understand the concept, or they're lucky enough to live in a area and have the money to afford using ungodly fast and expensive Internet connections such as Comcast 105 Mbps.
Wireless connections require configuration to prevent anyone with a WiFi in range of your router from connecting to your network. They could do malicious deeds, such as hack into your network, or just leech off of your Internet bandwidth.
Wireless setup is not too difficult, Just follow the instructions in the router manual or wizard set up program. If you're having problems either pay someone to set it up for you or find a knowledgeable friend to configure it. Once the wireless network settings are configured it's a fairly trouble-free system.
Good Luck...