In short, the meeting can go ahead with those in attendance forming the quorum.
And it is only a 75 percent vote (as calculated by unit entitlements) of those in attendance in person or by proxy that is required to pass a special resolution (in NSW).
For instance, if you have a general meeting in a block of 100 owners and only 10 turn up but eight of them vote in favour of the special resolution, then it has passed (provided the votes for are more than 75 percent of the unit entitlements of those voting).
That’s one of the reasons that special resolutions requiring a 75 per cent of the vote must be clearly identified as such on the agenda.