Let me explain (jf you haven't figured out what these things are).
These devices use the electrical wiring in your house in a similar way a hard-wired (ethernet cat 5 cable) does. Only slower speeds but fast enough to share an internet connection.
Most (if not all) wiresless routers have hard-wired ports as well so they are really dual purpose.
If I understand you right, you can't (or without great effort and expense) run an ethernet network wire from the main internet connection location to the other room. Is that right?
If so, you can try getting two of the powerline network bridges and see if that works for you.
You will still need a router to be able to share the internet connection. Even if you only had one PC on the internet a router is still a good idea as it acts as a firewall.
The connections would look something like this
The cable modem would plug into the WAN connection on the router. Plug an ethernet wire from the 1st PC into any port on the router. Plug an ethernet wire from the powerline bridge into another port on the router. Plug the powerline bridge into the wall outlet.
At the other PC, connect the powerline bridge to the PC with an ethernet wire and then plug it into the wall outlet.
On both PCs you should make sure that the network connection is configured for DHCP (IOW, to get an IP address automatically (from the router)).
After that, the two powerline bridges should automatically see each other and complete the connection from the second PC to the router. You should be able to access the internet now.
Lastly, there are wireless repeaters that will essentially extend the range between the wireless adapter on the second PC and the wireless router (they're called a WAP (wireless access point)).
I don't know how (if any) delay in the repeating process will affect online gaming but it's worth a try.
Try google for "wireless repeater".
Here's a link that explains more about wireless setups.
http://www.practicallynetworked.com/networking/wireless_bridge.htm