I think you're asking the wrong question. It's not can it support (your favourite distribution here), but can it run (your desired application suite here) reasonably with (number of users here) logged on, or queries per minute, emails per hour, etc. etc.
In general, GUIs take a lot of oomph (technical term) will run slower on older machines. In text mode, you can still do a lot of useful things with very old hardware. (Like a Pentium II 500MHz)
You could certainly get some ok results from a Celeron 2.4 workstation with a decent amount of memory.