I've had poor luck with a PVC "Rocket Tool". For cups that weren't too tight, it worked but got splintered on my second headset where the cups were very tight. Copper plumbing tubing is a better choice for a home made tool.

Nashbar sells a suitable commercial steel tool similar to the Park version but a bit less expensive: http://www.nashbar.com/bikes/Product...85_-1___202581