All the things mentioned can pretty much be done with every distribution (mainstream distro's that is). But it's not going to work out of the box! You need to configure most things manually (for what you need anyway).
A distribution is merely a personal choice to make. The glove that fits the hand sort of thing (or is it the other way around?
Some distro's are targetted towards the so called "noobs or newbies". Some are more for experienced users or people who like to dive into the deep of the linux ocean.
Some Free Distro's (not all are listed here) which are well known for server usage:
And the Unix counterparts
For the things you want, the following pops in mind:
- Have the server download all emails and distribute them to pc's running XP & Outlook.
Install a SMTP and a imap/pop3 server.
- Look at my emails remotely, either from my laptop or pda whilst I am away from the office.
Install a webmail script on the server (in conjunction with apache).
- Be able to access my files (stored on an external HDD connected to the server) remotely if I have to work from home.
Use a tunnel setup, to safely connect to the office from home.
- Hook it up to my Belkin wifi modem.
ehm.. check the HCL on this site..
- Secure the server from attack.
. Well it depends on de the daemons and such... but a good Firewall and up to date software is 50% of the security measures.
Read many howto's and advisories on certain services running.
Hope this will help you a little