Tylenol is fine for most dogs. However, just like humans, it is fatal in dogs when taken in overdose. However, dogs need less than humans, even after adjusting for weight.
The story posted earlier in the thread about a critically ill dog is because of a *massive* overdose of tylenol - literally 8 times the recommended dose.
The problem the OP has is that his dog is tiny, so the dose required would be tiny and impractical to administer accurately - it would be measured in drops of children's tylenol - and for this reason and the extreme harm from overdosage, it wouldn't be appropriate to use it - particularly as a vet should be able to suggest a more practical and safer alternative.