Protecting my data

[<duterium@blueyonder.co.uk>]

Hello,
 
Thanks for your all your advice about linux hardware etc.
 
I am looking for some advice regarding securing data on my server.
Basically I am building a server for my business, and I want my small number of users to be able to upload and download sensitive information from my server over the internet.  I have experience with many ftp server, etc, but not secure services.  My users are all running windows boxes.  The files will be all sizes, anything up to 1 gig each, maybe more.
Ideally I would also like the data encrypted on the server as well, to protect from any kind of hacking etc.
 
I have have used pgp for windows and i like the idea of my users having secure keys they can use to dycrypt the data.  Are they any good open source versions of PGP and can a similar system be used in my case.
 
Any adivce you can give me would be very much apprecated.
 
 
Pete Bainbridge