Firstly pretty much every 'ordinary' infantry, cavalry, artillery, chariot or whatnot in WHFB has a TW counterpart - orcs are just particularly tough and poorly disciplined heavy infantry and so on.

For magic http://diceofdoom.com/blog/series/wa...r-magic-guide/ gives a summary of the spells available - wizards generally choose one of 8 lores which have 6 spells each and these generally either act as magical artillery or augment or demoralise your own or enemy units and thus mostly have TW equivalent effects - a fireball from a catapult and one from a wizard are pretty much the same thing.

What is problematic in TW terms are the uber-powerful single heroes and monsters who have tended to get more and more powerful and unbalanced with each edition as GW decided that they'd rather sell insanely expensive metal special figures (a single chaos warlord figure will set you back £30 and an elf on a dragon £32.50) than units of plastic orcs or whatever - AFAIK there's no TW equivalent for a single godlike superhero mounted on a dragon or griffin who can just drop out of the sky anywhere on the battlefield and annihilate whole units.