Creating a Network Plan

Hello,

I have been invited to a second interview for an I.T support role and have been asked to create/present a network plan for five minutes during the interview. I have been asked to include the following details:

- Hardware to use (firewalls, routers, switches, phones, servers...)
- What i would use to link two buildings (both are very close to each other so digging to lay a fiber or copper link would cause minimal disruption, only have to dig across a car park, no roads etc)
- One particular department requires high speed access to their files (surely 100Mbps would be adequate, perhaps using certain QoS policies on the networking hardware would achieve this?)
-  All users (60 in total) need to have the following services available to them: Progress database, MSSQL2000 Database, Exchange 2003, Terminal services (only for 15 users), Sharepoint services v3, Domain controller(s), DNS+DHCP services, File server(s), Centrally controlled antivirus.
- Have to use multi-role severs where possible

There are approx 40 clients in one building and 20 in the other, external WAN links  are a 2meg leased line and 2 meg adsl connection.
 
Costing is not part of the presentation, but i think showing that i have considered a cost effective solution would look good. So i need to make an efficient, reliable and cost effective (as possible) network plan!

I'm asking for a little help, particularly on the server side of things (i'm not too bad with basic networking) just to point me in the right directon. Like how many actual hardware servers would i require to provide all of these services? If i proposed a small amount of really powerful ones and used something like vmware to create several virtual servers, would this be reliable/cost effective...is it possible to set up failover redundancy when using virtual servers? Are they any good in he first place? Are they easier to manage etc...

Would it just be best to have several hardware servers and make as many of them as possible share services, like one server could be both the exchange  and terminal services server etc...could one of the routers provide DHCP/DNS services or is it better to have a dedicated server do this?

As you can probably guess, i don't have much of an idea of how these services would be practically set up in real situations! Any help to point me in the right direction would be great!