I recognize this problem quite well, since they were fairly hard to beat when I first encountered one.
I used this tactic on them:
1. make sure your second skill is set to SNEAK.
2. Sneak just in the sight area of a single deathknight (marked red), then lure it away from others. If you venture too far away, the deathknight will turn around and resume its normal patrol. Use as much magic as you can, or just equip weapons you're proficient in and slash away! Use stat-potions if needed. I was a level 9 WARRIOR(hero) and MAGE(Deathknight) when reaching that level, so you shouldn't have a problem with them if you do it this was, even if you have divided your stats evenly.
Hope it works <img src="/ubbthreads/images/graemlins/biggrin.gif" alt="" />
