Setting Up An Wireless Network & Email Account?

Hi all,
I am about to setup a Wireless Lan in a small office environment (5 PCs -
Win XP) using a BT Intelligent Gateway Wireless 2Wire HG1800 Modem.

I have a couple of questions to ask before I start the installation;

1, I am thinking of having a 6th PC (without the Kb & Mouse) just for the
internet connection! Do you think that this is a good idea or would you
suggest some other way of doing it?

2, The company has its own domain and email setup ((E-Mail Removed)) so what
would anyone advise me to do regarding the setting up of the email i.e. use
SMTP/POP3 or some other setup (VPOP3)?

3, The BT Gateway/Router should provide me with all the settings that is
needed to connect to the internet and to provide a wireless connection to the
5 PCs but I would be gratefult if anybody who has had any connection with the
BT 1800 gateway/Modem to let me know what if any pit falls there may be when
setting up this wireless network?

I look forward to any suggestions anybody may have regarding the above,
please?

Regards
Gerryw