I agree with Sonnyjane, except I will make one disclaimer: It'a a Small World
may still be up. I wouldn't say for sure that it will not be up just yet. The reason I say this is because I was at DLR last October on the 24th, a Saturday, and we rode on IASW to look for the Disney character doll additions to the ride. But Vala, one of our great DIS-ers on this board, was at DLR a few days later - the 28th, I think it was - and she said that IASW was shut down by that time. So since you will be arriving on 10/23, which is a Saturday, you may possibly get to see IASW on the 23rd and 24th. I would
assume DLR would leave it up for that weekend and then close it down by Monday the 25th, probably.
Also, I should point out that last year's holiday/Christmas season at DLR began one week earlier than it normally had begun - on November 13, two weeks before Thanksgiving - so the IASW Holiday overlay had to be up and running by that date. However, if DLR goes back to its regular holiday schedule this year and starts Christmastime only
one week before Thanksgving rather than two weeks before, the 'regular' version of IASW could, perhaps, be up and running a little bit longer than it was last year, maybe until the end of October.
In any case, whenever the holiday season begins in November, I think you
may have a shot at seeing IASW in its non-holiday form on the first day or two of your trip, the 23rd and 24th, based on my experience last year. That is, unless those sneaky Disney people totally change up the schedule on us!!
One other thing - if you are a Space Mountain fan, there is a chance that the Halloween overlay for that - Space Mountain Ghost Galaxy - will return this year, so you will have a chance to experience that, as well as the cool Halloween villains-themed fireworks! Last year was the first year DLR had Ghost Galaxy, so based on its popularity, I could see it making a return. There is also talk of a possible Toy Story Midway Mania Halloween and/or Christmas overlay, but no one knows as of yet if this will happen this year or, perhaps, after the DCA overhaul is complete in 2012-2013.
In any case, Halloweentime at DLR is a great time to go and you will have a fantastic time! I hope you follow along with our Halloween at DL superthread, which is chock full of fabulous photos and information!

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http://www.disboards.com/showthread.php?t=2408927
ETA: Sonnyjane must have read my mind, because apparently she was typing her last post about IASW when I was typing this one!