There is no actual way of knowing if your company is checking on what you are doing. It depends on what software they use on the network and if they even check on it. If you are in Europe then they are supposed to tell you that they can see what you are doing as part of the privacy laws, I'm not sure about the rest of the world.

Even if they do not have any software to check and you connect straight through to the internet it is very easy to see where users have been. Cookies in you your profile get dropped at most web sites. The history in Internet Explorer will show where you have been as well.

Snooping on users is very easy. I would recomend that you only use the company internet connection for professional use. At the least get advise from a manager about what you are allowed to do, send an e-mail so that you get in writing that you can use the internet for personal use.

Take care in what you do.