I caught onto HTML pretty quickly, but didn't really pay attention to how things were changing when everyone started coding tableless so I had to learn how to do that. Honestly, learning it's not the hard part, becoming efficient at what you do is the hardest part of coding.

EDIT:: In regards to your question, you can code off of a screenshot the same way you do a PSD, just bring it into PS and slice away. It may be more difficult, but you'll get the hang of it.