Don't eat the stringy stuff--use the mealy flesh of the pumpkin, minus the rind.

Dunno about garlic and butter, but I have roasted seeds before--you have to clean the stringy stuff off, blot them dry on paper towels, and then roast in a single layer on a baking sheet. IIRC, I brushed the pan with oil, and partway through the roastign I stirred the seeds to roast both sides. You have to check them and take them out when they are light brown, before they get too dark.