Question : Proxy? Do I have to?

I'm not sure what category this falls under, I'm not even sure of terminology.

I need a way to monitor my users web browsing, I REALLY don't want to install a proxy as it slows the network down and requires that I reconfigure the network.  I also would like to add a web filter and any other sniffing, forensics apps I could use.  
We currently have none of these things in place and desperately need them to keep down on viruses and wasted time.
I know this is one of those "tyrant IT things" but it's necessary.

So the question:
How do I add these security and forensic tools without changing my network?  If that isn't possible how do I get by with minimal changes?

Answer : Proxy? Do I have to?

Depending on what Router / Firewall your using there should be an option for enabling web logging. Should also be filters to configure to block specific sites.

In a corporate environment this is usually done from the Firewall.