-Probaly the two biggest differences are speed and the ability to easily move a tool rest. You may want to spin the wood up to several thousand RPM, but metal work will never go that fast.

I have an old old companion wood lathe that can be used for light metal work. it has a tool holder on an x-y tabel to control it. You can take it off and put

on a regular wood tool rest also. Its vey light duty and I had to play significantly with the speed range

-The main "difference" will be in the toolpost/toolrest, which must be free-moving and adjustable in height for turning wood. Also, you should investigate the range of external spindle thread sizes that are found on woodturning lathes if you want to be able to buy the various accessories. On top of that, many metal lathes come with an internal headstock bore requiring #3MT with a tailstock that may be #2MT, and most woodturning lathes are #2MT for both (some of the minis are #1MT). Also, most metal working lathes I've come across are covered in oil and metal shavings, which would really create a sticky goo if you added a good layer of wood dust and shavings! Other than that, you can turn wood on a metal lathe. Try posting this to the rec.crafts.woodturning group, and you may find some who actually to this