Network Config!

Hi there, looking for some help on network design. Here is the situation:

3 – Novell servers, 2 / 5.1 – 1 /4.11 INTNW.
2 – Nt 4.0 servers.

We have about 200 + users who all use e-mail / internet. But here is my dilema 50%
of the usersuse multiple servers Novell + NT. We are currently using switch hubs and has been working fine, but now we are going to be adding more PC’s I am afraid of what might happen. I am looking at getting some new network hardware to prepare for the extra volume. I am looking at a Nortel 350
stackable switch so that I can segment lans & create some V-Lans to lower the traffic. Should I look at getting just 1 Switch? Or should I get more than 1? Any help would be appericated.
Thanks for the help JT