Any distro would be fine.
With some of the more bloated distro's you'll need to turn off all of the unnecessary services to get to what I would call an acceptable speed. You may find the normal desktop environments to sluggish so you could switch to a lighter one like xfce, or even just a plain old window manager like fluxbox.
Please, please do not fall into the trap of thinking that you can only put older software on older machines, your just storing up problems for yourself. You shouldn't be using old unmaintained software that has bugs and security issues that have since been addressed. Remember this is not Windows, Linux scales very well.
Also your hardware isn't
that old, its plenty to make a good, stable, usable workstation.