Bill....you will not be disappointed with the D90. It has many of the functions of Nikon's "pro" model D300, and since it is a newer release, has a few extras like video capability. The image sensor is virtually identical to the pro model, and may be just a bit better regarding processing the image, depending on what file type you choose to shoot. Memory cards are cheap right now, and many have nice rebates, so I would recommend getting a couple of 8GB, high speed cards made by either Lexar or SanDisc. The higher speed cards allow the camera to write data faster so there is no lag time when shooting multiple shots in sequence. There are cheaper cards out there, but IMO those two brands are the best and most reliable. With the two 8GB cards, you will be able to get over 600 images, even if you shoot them in RAW (largest) format. If you shoot in Jpeg large, you'll be able to get well over 1,000 images on the two cards. On the back of the bike, Jpegs will do 90% of the time. For scenic shots, the RAW format will record more detail in the highlights and shadows. The D90 is capable of many things, so there will be a learning curve involved to utilize all the functions, but you can also just pick it up and shoot with it if that's what you want to do. It doesn't HAVE to be complicated, but I would recommend playing with the camera and figuring out what kind of settings you like and set them up in the "my menu" so they are easily accessible without digging through layers of menus to get where you want to be. The D90 has an outstanding LCD and it can also be used in "live view", like a point and shoot without a viewfinder.
Regarding the Nikon 18-200 VRII...it is a great all purpose lens, and IMO, superior to third party lenses in it's class. You will likely use the lens more in the 18-135 range, which is where it is at it's best. At 200, it's just a little soft, but nobody but an expert would be able to tell the difference in anything other than a very large print (larger than 13x19). The VR will allow you to get shots that you normally would not be able to get with a non VR lens. It is also a very fast autofocusing lens because it is an AF-S lens. You will be happy with it...Nikon has sold nearly 1 million of these lenses, so they must have done something right. I am a firm believer in putting a protective filter on all my lenses, but please do not cut corners on this item. I personally use B+W skylight or clear filters with their MRC coating which ensures that the filter will not degrade the image quality you are paying for with the Nikon lens. Hoya is also a good brand. I'm not a big fan of Tiffen. You'll pay from 70-100 bucks for a good filter. A polarizer would be a good thing to have as well, for use off the bike....again, don't scrimp on that glass either. I get almost everything from B&H Photo in New York...they are reputable and have good prices. Good luck, and enjoy your new camera!