There are many points and kinds of statistics one may want to monitor on a server (Or a desktop PC), the following are a sample of the things people commonly need
1- By Domain name, when you host people’s websites, you need to monitor there traffic, both Email and web, it may be worth mentioning that the only way this can be done is through log filres, he reason behind that is that HTTP and Email requests are pointed at IP addresses and Hostname (Domain name) is only available as data within the stream, something only parsed by the web server and the MTA (Mail transfer agent). Some software to analyze Log files exists and can give you the answers to Domain based network traffic.
2- By PORT, Ethernet card, and IP, For such uses i recomment IPTRAF for live monitoring, and ….
3- By Virtual machine in environments such as XEN, in that case you can use the ifconfig command to see every virtual adapter’s traffic usage.
I will come to this post with more soon.
NOTE, for windows network captures (packet sniffers), i have always used a windows utility called wireshark (previously etherial), Microsoft released a very similar utility called Microsoft Network Monitor 3.4 that is compatible with Windows XP and above, When i simply want a graph of usage, i have once used a utility that does the trick called bwmonitor that is for $25, but it does provide you with a 30 day testing period (There is certainly a different application that can do the job and most probably a free one too, i just used this because it was the first i found)