for some reason the tainted magic tab is not appearing in my thaumcraft book ?

Yeah, most likely just an overloaded Thaumonomicon. Check that you don't have too many addons installed!

There's also a nice addon that allows for extra tab slots if that is the actual issue.

Yes, I do recommend Not Enough Thaumcraft Tabs.

This question lacks information. Did you perhaps overload the Thaumonomicon, causing it to not display any extra tabs? If so, go install http://minecraft.curseforge.com/projects/notenoughthaumcrafttabs
I am certain that Tainted Magic's Tab displays correctly.