soma56, I suppose I could just suggest that you slap a firewall up, configure the rulesets properly and forget about it but, I'm not. For starters, I don't even know if you have a firewall. There's always a chance that you do and have it set to allow most traffic. I'm not clairvoyant you know .
Instead, I can start you off with some investigative tools to better help you figure out what traffic is floating in and out of your computer. These are basic tools, since you mentioned ethereal was a bit too complicated.
These two programs are very basic for monitoring your traffic:
Port Peeker
TCPView (I use this one)
(I recommend checking out other products from WebAttack.com because they have a lot of nifty programs). You can use these tools to see what is opening your ports. Remember though, these aren't pro-active protection, they're just simply traffic monitors. elmurado also suggested a great idea. Get to know what services run on what ports. It will help you vastly to understand the traffic monitor logs if you at least have a reference to what ports are associated with.

Another angle to approach is to download some kind of active process monitor, such as TCActive, which comes bundled with The Cleaner. There are a ton of these kinds of process monitors, TCActive just happens to be one of my favorites. Once you have an active process monitor, you can go to a site like AnswersThatWork and check out what's running on your pc. Another great site is Windows Process Library. This is just one of many more investigative tools to better help you understand what may be opening ports on your pc.

Now, if you don't have a firewall, I do recommend you get one sometime soon. You can play around with the tools I gave you but, in the meantime you should get some protection going on. You have a wide selection of good names such as: Sygate, Kerio, Zone Alarm to name a few. All of these firewalls are listed here and they are free.