I work at an ISP [plug:
http://www.hpi.net] and our setup consists of the following in our central NOC: Cisco 4500, 4x Cisco 2600, 8-way osicom dsu/csu, 4x Cisco 2948G, a 3com superstack of some sort [for colos], 2x Ascend 4096 RAS units, 4x web servers, monster db server, misc utils machine, accounting machine [running Logisense's "Hawk-I" -
http://www.hawk-i.com and Funk Software's Steel Belted Radius -
http://www.funk.com], 3x dec alphas [just do routing/firewalling], plus 8 workstations and a couple laptops running around.
Now, that really isn't that much. We have < 3,000 customers. I've seen NOCs 50x the size of that, but to get started from scratch to be just an ISP would put you right around $18,000 in the hole. And that's running barebones. Right now, we have a scratch more than $100,000 of hardware in our WHOLE ISP. Monthly expenses for our uplink [10mbps through e-spire] and our backup [3mbps through qwest], our offices, our wireless roof-rights costs, hardware upgrades/reparations, etc. cost right around $18,000 a month. That doesn't include employee costs, blah blah blah.
It's a pretty serious undertaking, and sure, 3-5 guys can run a small ISP like us with out a huge problem, but I'll tell you -- it's not a small undertaking at all. Being a business major, I would advise you to create a business plan, a corporate strategy and an upfront design and implementation model before even *thinking* about doing anything.
Randal