They can naturally use either a fireball or lightning bolt
They have access to all the spells listed in the rules
They need to roll on the Spell Complexity table when casting
They can counterspell (or be counterspelled)
They can use magical weapons(!)
That's mostly it, I think. I'm making this up as I go, but I'm also going to allow any Hero or Wizard to have up to 3HD of followers, human or otherwise.
Depending on how it goes, I may limit the number of Wizards who can participate in a single adventure... I'll likely tweak other details as well (like allowing a choice of being able to turn invisible, use ESP, or levitate); we'll see!
We just finished playing, and it's funny you asked that, because, no, I didn't use that rule on the Fantasy Combat Table, but I'm leaning towards it for next time... I'll be writing up a summary on ye olde blog...
"He was one hundred seventy days dying and not yet dead."