Ok, I've tinkered with various linux's over the years but never really got into it, I'll try to make this brief.
Upto a couple of months ago I had a headless Win98 workstation running as a mailserver/client, I now have a new

box and am thinking of doing the same with that.
Specs:
Celeron 500Mhz, 128Mb Ram, 6Gb HD, DVD reader, CDRW. (Did I say it was new

).
Requirements: You tell me

Headless, My desk can handle two boxes but not two monitors/kb/mice and I can't be bothered with a KVM switch;
Security, as it's planned to be a mailserver then this is paramount, initially it will be behind my router but the plan is to move it in front and be part of the firewall *that's probably important*
Before I used a VNC viewer/server to control the w98 station and I'm hoping to do the same with the linux box without having to use X11 etc
I'm not a newbie with computers but TBH I feel like I will always be with Linux (Information overload anyone?)
Suggestions?