Network Bottleneck

Network Bottlenecking

How can I monitor the network for bottleknecking. Every Monday and/or tuesdays our network is so slow. Is there a way I can pinpoint what going on here? Free tools?

The entire network Slows Down when anyone does a download from the internet

I have a full T1 line from AT&T that they continually test as good. There are (3) companys on the same T1 My company has a Windows 2003 Domain, (3) servers (Exchange 2003, Connectwise and a Citrix server). On average I have 5 users on my network. But the problem occurs even if there is only one...