Limit Internet download access

I run a small 25 user LAN for a CPA office and have been running around lately fixing PCs getting hung or having other problems. I have a Novell 5 network… not running Zenworks. I have noticed icons in “systray” on some the workstations that areprograms downloaded from the Internet… such as Webshots, weather bug, gator just to name a few. Does anyone know of any way I can limit the download access behind the scenes? Any free software available. The workstations run several tax programsvia the server and the downloads just complicate things.

thanks,
Rob
CNE3,CNE5