Hi Jaci,
The easiest route is from the north, but you might have to park a bit further away - I'm not a driver so not sure of the best place to park up.
If you haven't already, it's worth looking at a 1/25000 (Explorer Series) Ordnance Survey map. You can see the general area here: http://www.hill-bagging.co.uk/bingmaps.php?qu=S&tu=Y&nm=trendrine&ct=EWM - it's centred on Trendrine Hill, which is a little to the ENE of the Quoit.
The Eagle's Nest is a house by the road - it's where the label "Higher Tregerthen" appears on the OS 1/25000. The driveway to The Carne is on the opposite side of the road, you can see it as a double pecked line on the map (not shown as a footpath, but the whole area is access land so you can wander).
As the driveway heads south from the road, it forks. The right fork (the driveway) continues to The Carne, the left fork (a track) goes to Sperris. You can take either, Sperris Quoit can be reached via the left fork, near some ruined mine buildings. If you go to The Carne (which is derelict, or was when I last went), turn left (south-east). The Quoit is on the right of the path heading this way.
Hope that helps with route-finding.
You can approach from the south or from Beagletodn to the SE, but these tend to be a bit more overgrown in places.
One other word of warning, it can quite often by misty or mizzly at Zennor, which can make route-finding a bit trickier if you don't know the area.
