Hardware Firewall setup help

I am so confused by opinion and information about protecting a small business network with a hardware firewall. Can you please help?

General layout
T1 feed to Cisco 2600 to eth0 and eth1 circuits. 12 Win flavored servers and one RHL.
Currently protected by individual software firewalls.
Webservers, DNS, Email, Media Streaming, Web surfing.

Objective
To include hardware firewall wherever it should be best placed and setup said firewall so that it protects the whole network. Never done this before.

Area of Help
To provide a step by step guide, avoiding hand offs to over-technical or out of date instructions.

My experience with Linux is very limited but I believe with the right help that
I can do this installation.

Choice of servers with two nics

Pentium 333 with 384 Ram 8GB hdd

or

AMD xp 2400+ with 512 RAM 75 GB hdd


Starter questions
If I can avoid slowing traffic through firewall would "faster and newer" be better for Firewall?
What OS do I download and how should it be installed?
How do I test the firewall is ready for placement in the network?
Where do I put the Firewall - before the router? (router has two circuits out)

It would be great to achieve this objective without making the mistakes
everyone before me did.

Thank you for your consideration.

This subject matter has been dealt with in another part of the forum.

Administrator please remove thread

Thank you