Yes, the definitely stack, but you can't put more than one enchantment of a single type on a single item (so if you want multiple health regens, you need to enchant on different items).
BTW - health regen enchantments require malachite gems (extremely rare) regardless of their level, so it's really only worth doing them once you have the level 10 enchantment. Items with even low-level health enchantments already on them are therefore more valuable than other enchantments, especially in the earlier stages of the game. (Level 10 health regen is 0.3%, copared to 0.225 for level 9).
Also, disenchanting items at your battle tower means you automatically learn the enchantments. So be on the lookout for any item that regenerates health at 0.3% - that's how I learned the level 10 enchantment.
Finally, the +100 health (level 10 life line) enchantment to armour is a better way of spending malachite gems than health regen. I have all four of my Dragon Wizard armour pieces with +100 health, which increases my total health by 50% (at level 45). Not only to I get more total health, I get +50% health regen (as health regen is always a percentage of total health, so +health = +health regen).
The other best level 10 malachite enchantment is +damage. I have +100 magic damage on both my (dual wield) weapons - I never fight melee, but +200 damage to all my spells (including each magic missile) is very useful.
EDIT: And how do I know? The damage enchantments are easy, just a matter of maths when you attack a relatively low level monster. As for health, I now regenerate so fast it's like a permanent healing spell, and the difference is noticable when I remove certain items.
Last edited by Trippy; 23/12/10 04:21 AM.