What do you think is the best Linux distro for me?

The specifications of what I will be running it on:

2.6ghz Pentium 4 HT (soon to be 3.2ghz)
768mb RAM (will upgrade gradually to 4GB)
32mb nVidia Riva TNT AGP card
Integrated AC'97 Audio
120GB HD
Intel Pro 1000GT Ethernet PCI card

What I want to be able to do:
Use blackbox/fluxbox as window manager
Set up file sharing fairly easily (and be able to install Netatalk)
Video Splicing
General Web Browsing/Chat

Other than that, there is nothing else that I need to use this computer for. I want the distro to be as quick as possible, and I also do not want to be shielded from using root if I have to. I would like it to be stable too, and have packages that take virtually no effort to install.

U should look at Ubuntu , SUSE or Fedora. I won't filter out more, cause it depends on you. Ubuntu is widely used and Fedora and SUSE are too...

And when its question of window manager, you can install whateva u want at any time

And no issues with file sharing, but maybe with Ubuntu cause its REAL END user's linux... sometime i feel that...

why dont you try several distros with your 120G HD? let's say ..20G per distro

The best thing might be you try the distros via LiveCD. So you se if you like them before installing them.
But your Computer ist relatively strong and so nearly all distros will run fine with it.
My favorite distros up to now are
big: Mandriva, Ubuntu
medium: Knoppix, SamLinux, Openmamba
small: Puppy

Sometimes it is really difficult to say which one I like best.
Puppy I know best and it worked on old and new PCs fine but only in English
Knoppix it is in German,
SamLinux Multilingual and
Openmamba in Italian or English
Mandriva and Ubuntu are Multilingual.

I don't know what do you expect from a distribution.

My recomandation is to check them they are all relatively easy to understand have online-manuals and forum-support.

Have a nice day