You can use all three methods-- knock 'em in with a hammer and block of wood, use a homemade press, or use the tool. You can screw up with all three, too. No matter which method you use, take your time and make sure the cups are going in straight. If they're not, knock out the cups and start again. Patience. When done, hold the frame up to the light and make sure the cups are flush with the head tube... as others have stated, grease the cups lightly where they insert into the head tube.

I've done all three; personally, I prefer the real tool. But all three methods work, and none of them is superior to the other two. The key is taking your time and doing it right.

For knocking cups out, nothing beats a headset rocket, but you can use a length of copper pipe with a smaller diameter than your head tube.