im pretty computer illiterate but how can "they" tell where you've been?
if you delete cookies regularly will that help?
It can, depending on how large the organization is, what kind of network infrastructure there is, the kinds of network reporting software used, and how pedantically intrusive the policy requires them to be. Them, being the IT department. Lots of factors other than mentioned, too. In generally, deleting cookies will only 'help' in this regard if the extent of their infrastructure is a cable modem and a single switch - or, say, in a network environment with no dedicated support or administrative staff.
Your outgoing and ingoing traffic can basically be intercepted, monitored,
modified at any point 'upstream' from your physical connection point. This includes and is not limited to the network switches, monitoring servers, proxy servers, the gateway, or even outside the corporate network (though usually not by the company themselves). They can aggregate connection statistics for each user or a group based on web site, user, computer, IP address, time, and a dozen other things. They can monitor HTTP (ie web site) data flow real-time - for instance, by monitoring the network and viewing every image that goes through a given switch, router, or other network mechanism. They can do this all at the click of a mouse using readily available software (some of it free).
This does not apply to encrypted connections, though such connections have their own inherrent problems (ie it can draw suspicion to you if you're not in IT and don't have a particular reason to be using encrypted http/web connections - generally, they're just used for shopping carts and other such practices).
A proxy basically allows you to use a single connection point outside the network, bypassing any internal network proxys (which are where they ban material), with your own set of filters (if you want - you can do some neat things in this manner if you've got the knowhow). Open, anon proxies are generally filterless, but also fairly slow and unencrypted, so they offer little advantage while not encrypting the data and pushing all your connections through a single point - something which will set off an alarm if they're watching for such behavior.
What tor and torpark do is create a distributed, encrypted proxy network; in the case of torpark, it will not save any cache data whatsoever, either. Tor is a standalone proxy distrubution package, and Torpark is just a slightly-repackaged versions of firefox with tor built-in. If you use either of these programs, all your web connections will be routed somewhat randomly around the world, encrypted, to other Tor and Torpark users, who will then make the web page requests to the servers, and send the resulting page back to you. Each new request will likely be through a different host, if it's available. It's slow, but generally fairly reliable, making your Internet trail all but untraceable back to you from the servers you're requesting data from. However, a competent network administrator will still be able to recognize the useage pattern of Tor, and may call you on it - though knowing the mentality of most competent admins I've met, I'd say the chances are slim, short of making sure you're not looking at child porn at work or doing something to undermine his network security.
And here I was hoping I might get to visit some other sites. 
