192.168.1.254 will be your internal ip address. Because it is the last available in the ip address range it looks like a static ip address could be assigned.
Port 137 is netbios which is needed for your pc to communicate over a LAN. Although strictly not a necessary process I believe it is a necassary process to communicate with the gateway / router to connect to a WAN or internet also.
68.142.233.74
68.142.233.76
Neighborhood
Host : stun2a.voice.re2.yahoo.com
Country : United States
It looks like yahoo is doing something of its own accord in the background. I wouldn't worry about it too much although I prefer to control what has access to the net, so for me, I would disable yahoo from startup in msconfig and just start it manually when I need it.
Here are two ip lookup sites:
http://ip-lookup.net/index.php
http://ws.arin.net/whois/
Here are two port description sites if you want to research what port is being used and why (the second link lists exploited ports and offending processes. Keep in mind legitimate processes will use these ports also):
http://www.donkboy.com/html/ports2.htm
http://www.iss.net/security_center/...