Are there any resources on the web or in print about running or converting the classic adventure 'Tomb of Horrors' in D&D 4.0?
There's the hardcover Tomb of Horrors superadventure, which is readily available in stores. It's not a strict conversion, however -- more of an update. Instead of being one adventure, it's a series of interlinked short adventures which are intended to take place over the course of a group's career.
Earlier this summer, WotC sent out a pure conversion to people who'd registered for the DM Rewards program. It's a superb product: it retains the trap-oriented focus of the original, and it's far more deadly than I would have expected from a trap-oriented 4e dungeon. Unfortunately, these rewards are a one-time thing and it probably won't be sent out again. I'm sure it's available on EBay at fairly high prices.