Sun Microsystems Netscape Enterprise Server Administrator's Manual page 264

Sizing Issues
Next decide how long the average user will be willing to wait for a document,
at peak utilization. Divide by that number of seconds. That's the WAN
bandwidth your server needs.
For example, to support a peak of 50 users with an average document size of
24kB, and transferring each document in an average of 5 seconds, we need 240
kB/s - or 1920 kbit/s. So our site needs two T1 lines (each 1544 kbit/s). This
allows some overhead for growth, too.
Your server's network interface card should support more than the WAN it's
connected to. For example, if you have up to 3 T1 lines, you can get by with a
10BaseT interface. Up to a T3 line (45 Mbit/s) you can use 100BaseT. But if you
have more than 50 Mbit/s of WAN bandwidth, consider configuring multiple
100BaseT interfaces, or look at Gigabit Ethernet technology.
For an Intranet site, your network is unlikely to be a bottleneck. However, you
can use the same calculations as above to decide.
264 Netscape Enterprise Server Administrator's Guide