As eladrin/drow have the "trance" ability, making them not need to sleep to rest, but instead enter a meditative state, are they affected by any kind of spell that induces sleep?
Yes, Eladrin lost their immunity to Sleep spells. Mainly because there aren't any Sleep spells any more...
There is still a Sleep Daily power, but there is no specific rule in either the Eladrin or the power to say they are immune. One of the many changes in magic from 3rd ed to 4th ed.
The sleep spell affects any creature that is not immune to slow and if they fail the save, unconscious.
Eladrin are not intrinsically immune to either of these conditions, so they are affected.
The way that 4e works, unless a creature explicitly states they are immune to a condition, they are affected by it.