Jofm5,
Congratulations on going Nikon, don't listen to the Canon types.
Ref. lenses.
My suggestion would be to look at the fastest lenses your budget allows, this will give you more flexibility in conditions where lighting is, shall we say, less than adequate. This is even more important for you because of your choice of a D100 rather than something more modern such as a D300 where many improvements have been made in sensor technology.
Also, try to stick to "AF-S" types rather than plain "AF", "AF-S" focuses so much faster !
If you can't afford the fast lenses, then the next best are some of the fantastic "VR" ranges, which will help eliminate some of the shake you would otherwise get in low lighting.
The 18-200 is a great consumer lens, and as a general holiday/family event lens, it's more useful than an 18-70, which you might find limiting when you're trying to grab some snapshot moments.
I am assuming you are in the UK, in which case I would suggest you try somewhere like Greys of Westminster. They've got an excellent second hand range that's all in pretty good nick, and if you ask them nicely they might let you try them out for a weekend before commiting to a purchase.