All of this is very good advice, and like many of the previous posters, I too have been down the same road as we all started new at some point in time.
When I pulled my first DSLR kit together, it was the D50, the Nikon 50mm f/1.8 for low light, the Nikon 18-70DX, and a Tokina 75-300. I figured I had the whole range covered. This worked great for me when I was very purposeful and was planning my shoots, and I figured I was set for a while... until the first time I went to WDW with this kit. My shooting mode changes in WDW; I can't compose or plan the shots was well as I can when being by myself, so I tend to shoot more in "snapshot" mode and/or "machine gun" mode. I found that I was constantly swapping lenses and it drove me crazy. The 18-70 was never quite long enough, and the 75-300 was no way wide enough. So after that trip I went looking for a mid-range zoom.
I wound up with the Nikon 24-120 VR. On a Nikon DSLR this is like shooting a 36-180 on film, which most people would consider not quite wide enough for a mid-range zoom, but it worked great for me. I would have considered the Nikon 18-200mm, but at the time they had just come out and were going for $1000 on Ebay as it was next to impossible to get one from a dealer in a timely manner.
I used the 24-120 for almost 2 years, and just recently swapped it out for the new Sigma 18-200 HSM OS (similar to Nikon's AFS and VR) for my general purpose walk-around lens. It's not as sharp as either my Sigma 10-20, or my Nikon 70-300 VR, and it has more distortion . But it is a great compromise, and hands-down better than the Nikon 24-120 VR. I got some awesome shots on our recent trip to WDW and on the
DCL Disney Magic.
All of this is a long-winded way of suggesting that if you plan on using your camera at WDW, the 18-135 might be the better way to go. Compared to a P&S, $650 for an entry-level DSLR and lens combo may seem like a great deal of $$. But in actuality, that is a pretty darn good price for getting into a hobby that will only cost you thousands upon thousands of $$ in the future. Which is Nikon's plan all along...
Just be aware that this is just the beginning.... sooner or later you'll be looking at things like the 200-400, or the 85 f/1.4, or the D300.... NAS
WILL strike!!