If you have the spark plug wires back on as they were before you removed the head, you need to open the timing belt cover, remove the timing belt and turn the camshaft EXACTLY 180 degrees clockwise from where it is now. Re-install the timing belt and everything will work.
The thing to remember is that the crankshaft turns twice to every turn of the camshaft.
Following the various manuals, they will tell you to make the arrow marks on the cam and crankshaft point up, which is correct.
Sometimes the camshaft has two "arrows" - or you try setting the crank and camshafts so the arrows point at each other (up and down) via instructions in some voo-doo BS Internet post. The result is that the camshaft ends up 180 degrees off. The lazy fix for this is to re-wire the sparkplugs 180 degrees out to compensate. Bogus idea in my opinion... EDIT: (sorry Rhinoman) The right way cuts down on confusion down the road when you have to work on the engine again...
Hope this helps!