In an interview with Entertainment Weekly, here's what Damon Lindelof had to say about the season finale:
"It will make you realize that the house you are standing in actually has a lot more rooms than you thought when you came into it."
To me, that sounds an awful lot like the description of a TARDIS.
I believe there is a definite connection between 'Doctor Who' and 'Lost', which I plan to share after this season of 'Lost' is over, but I don't think an actual appearance by a TARDIS is in store for the May 23rd two-hour finale.
I was originally planning on waiting until the entire series was over before I revealed my theory, but 1) someone else might beat me to it (if they haven't already), and 2) who knows if I'll be still around by June of 2010?
But I do have this theory of "relateeveety" I can share which could connect 'Lost' to 'Doctor Who'. In "Revelation Of The Daleks", there is a toadying amenuensis named Vogel. When I watched the adventure with Mark & Michael last week, we all came to the same conclusion: despite the passage of many millennia, Vogel would have been able to trace his lineage back to Ben Linus, leader of the Others on the island!