Here is how I was taught to make them - as Lydia said, low and slow.
Roasted Pumpkin Seeds:
Preheat the oven to 250 degrees. Carve your pumpkin and sort through all the pumpkin guts for the seeds. I use a large bowl to put all the cravings in and then place the seeds in a large collendar. Once I have everything sorted, I run cold water over them and pull off any remaing pumpkin pieces - you can also let them soak in cold water for about 15 minutes.
Remove them from their bath, dry them a bit and spread over a large baking pan. Generously sprinkle the seeds with salt and drop pats of butter over them. Bake for about 3 hours, turning them every 45 minutes (or so).
They should be brown (not burned/black) when done. Remove from heat and allow to cool. Enjoy!
I was also playing with the idea of making a sweet version this year by adding cinnamon and sugar (with the butter) instead of salt; my son would have none of that though.