while it's true that propoxyphene napsylate (the active ingredient in Darvocet-N, what you have) is generally regarded as having very little desirability as an opioid to most people, there are a few that actually enjoy them. If you have no tolerance, and very little experience with opiates in general, you may be able to catch a slight buzz from them.
Don't expect too much from 100mg, it is a relatively small dose. It is smart to test the waters with a small dose first though, some people find this drug very unpleasant. Assuming you have no negative reactions, you'll then have a better idea of how much to take next time.
I wouldn't worry too much about having a fatal overdose with the amount you have, as long as you don't combine it with any other CNS depressants. I think the biggest risk you would face is the increased likely hood of having a seizure. Propoxyphene is known to lower the seizure threshold. It should not be taken by epileptics or others who are susceptible to seizures. Also, it should not be taken by those with liver disease. Both propoxyphene, and the acetaminophen it's combined with, are known to be toxic to the liver, especially with high doses or chronic intake.
As for a "recreational" dose for Darvocet-N, I would recommend 300mg for those with average sensitivity to propoxyphene. While this dose may feel too weak, I would not recommend taking more. The effects will not become more recreational with increased dosage, and there is a very fine line between a good amount and an amount that will cause negative (possibly dangerous) side effects.
Personally, I probably wouldn't take Darvocet again. My last encounter with it was quite frightening. I had used it several times before in the 100-300mg range, finding it a mild but pleasant, so I thought I would be okay dropping 500mg at once to get a better buzz. Instead of the mild opioid buzz I was expecting, I was hit with strong nausea, dizziness and anxiety. I actually fainted while in a crowded coffee shop, and my friend who I was with said I had some convulsion like movements while falling to the ground. I recovered shortly though. The realization of what happened gave me a massive adrenaline rush, I popped up from the floor and made a quick exit from the store. I felt the normal Darvocet buzz for the remainder of the experience. It was quite frightening and turned me off from Darvocet thereafter.
be safe, and have fun.