What's your Cocoa experience?
What other standard Cocoa classes have you subclassed and overridden drawing for? How familiar are you with the low-level text rendering system?
Do you have an algorithm for inset text and inner shadow?
Depending on the overall context of what you're trying to do, I'm wondering if a webview with CSS-styled text might be a better approach. Googling the title of this thread shows a number of CSS solutions (or possible solutions), including posts on stackoverflow and other Q&A sites.
Overriding NSTextField's drawing code is almost certainly the last thing on my list of things to try. Second-to-last is probably "Find another visual effect" because inset text with inner shadow is too damn complicated to be worth the effort.