PC/electronics help needed

Greetings all.

Assume for a moment that I have no knowledge of electronics (not true,
but I only know what I've picked up and that's rather patchy). I'm
looking to make a little addon for my PC and I need a little help. I'm
after making 3 time/date displays using 7-segment (numbers) and
10-segment (letters) LED displays. One of them should actually show the
correct time, the others I'd like to show other static times, preferably
with the option to change them occasionally. The latter parts should be
within my reach but the actual clock is a bit more of a problem, our
school was a bit crap and didn't actually teach us how to do that.

I'd rather make it from scratch but I'll butcher an alarm clock if I
have to.

The other thing is that it needs to be powered from the PC's power
supply, so it'll need to run on either 5V or 12V, with some form of
battery backup to power just the real clock when the machine is switched
off. If somehow it could be made to display the system's internal time
that would be wonderful, but not necessary.

Any help at all would be vastly appreciated.

DjBx