Sounds like a great undertaking...
1) Good design states that you should plan for around 10-25% growth, so 80 users will mean you'll need about 100+ potential "network connections" (80 + 25% (20) = 100)
2) Divisions = VLANs = Subnets: If you wish to segregate your Admin, Sales and Design folks from being able to fully acess each others data, then you'll need to set up a seperate VLAN / Subnet for each department (break out that VLSM)
3) Equipment needed:
- Forget about hubs, they are antiquated and cause more problems than they solve in networks and wont meet your through-put requirements.
- Switches are a must. 80+ user connections, VLAN/subnet segregation (and even some PoE) are what switches live for. In your case, a few 48-port or multiple 24-port switches would be ideal (PoE if you ever go with VOIP)
- Router - Also a must: its how you get all your users from the Internal LAN to the Internet, how you allow necessary traffic (DNS, DHCP, Voice) to flow between VLANs/Subnets, and how you filter unwanted traffic between the same
- Cabling - Kind of a given: Standard Cat5/6 will do you nicely. If the departments are geographically seperate, and there is cause for it, Fiber works too
4) To meet all of your data rates, allow for growth and provide some cushion for those data usage spikes, Gigabit Switches / NICs are best - you can even "aggregate" links between switches for a nice little 2-8Gigbit inter-switch "trunk"
As always, the best, honest answer for any Network design question is: "It Depends".
Lastly, Fit your design to meet not only current requirements, but allow for growth (VOIP, wireless, Tele-commuters, more users, more servers, Applications, etc)