I'd propose that he has a slightly different plan. I'm going to give you my pet theory here so hold onto your hats.

I think Quirrellmort probably decided at one point in the past that it would be way easier to take over magical Britain if everyone thought he'd already failed at doing so. I think he's probably going for control of both sides. Imagine if Darth Vader had created the rebel alliance in order to funnel potential opponents into a harmless straw-opposition: he could let them attempt the occasional coup, always avoiding any real cost to himself and throw them the occasional minor victory to keep them on the hook.

To quote the chapter Contagious Lies:

"Yess," Harry hissed dryly, "very amussing, I am ssure. Except now am sstuck in Hogwartss for next ssix years, for ssafety! I have decided that I will, indeed, sseek power; and confinement iss not helpful for that. Musst convince sschoolmasster that Dark Lord iss not yet awakened, that esscape was work of ssome other power -"

Again the rapid flickering of the snake's tongue; the snakish laughter was stronger, dryer, this time. "Amateur foolisshnesss."

"Pardon?" hissed Harry.

"You ssee misstake, think of undoing, ssetting time back to sstart. Yet not even with hourglasss can time be undone. Musst move forward insstead. You think of convincing otherss they are misstaken. Far eassier to convince them they are right. Sso conssider, boy: what new happensstance would make schoolmasster decide you were ssafe once more, ssimultaneoussly advance your other agendass?"

Harry stared at the snake, puzzled. His mind tried to comprehend and unravel the riddle -

"Iss it not obviouss?" hissed the snake. Again the tongue flickered sardonic laughter. "To free yoursself, to gain power in Britain, you musst again be sseen to defeat the Dark Lord."

That's obviously not the same plan I'm talking about, but we can see that Quirrell has at least been thinking along similar lines to me. I can see a number of different ways he could have formulated this plan, but the simplest one seems to be:

• Set up evil organisation and make an attempt at taking the country over. Allow everyone to gauge your intelligence from your actions, and to form the strongest alliance they are capable of forming against you. Everyone's gauge of your intelligence will in fact be off by several points, since this isn't really your big ploy - it's actually a feint and you intend it to fail.
• Fake your own defeat, simultaneously creating a (young, impressionable) hero for your opponents and removing yourself from all further suspicion, since almost everyone will think you're dead.
• Become a role model to the aforementioned young hero and mould him to your will. The kid is in the perfect position to take over the leadership of your opposition, so you now effectively have control of both major players in the game.
• Win.

This is also foregrounded in Coordination Problems 2 and 3. Quirrell wants Harry to bind the population together under him and Harry makes a short speech about the dangers of group thinking. Quirrell's reaction is one of anger - obviously he can't have Harry breaking the monopoly that the Order of the Phoenix has on do-gooding, because that opens the field up for thousands of free-agent challengers to Quirrell's power. It also mirrors Harry and Draco's plan to play the two sides off against each other, except obviously Harry is aiming for world optimisation, not domination.

Finally, Dumbledore seems to think Voldemort is still alive, but he's either pretending to have irrational justifications for this or he really does. I think it's waaaay more likely that Dumbledore is just playing dumb, since he's definitely smarter than he lets on, as evidenced by his and Snape's big discussion about the Bellatrix thing, but I'm not entirely sure how much Dumbly knows for sure. Quirrell knows Dumbledore acts as though he thinks Voldemort is still alive. The real wildcard is Harry, because Quirrell probably wasn't expecting him to be such a major agent in all this, he's almost certainly playing Xanatos chess at this point trying to keep ahead of Harry and keep his plan alive.

Or at least that's my theory.