Why get an 18-200 when you have an 18-55 already? It's pointless to have two lenses with you that overlap, especially if one has the entire range of the other. If you're selling the 18-55, then you should probably get the 18-200.
You can get a 55-200 for $250 instead, and since you're new it shouldn't matter what the minimum aperture is. Just focus on the photos, not the gear. Check the 55-200 out here:
http://www.kenrockwell.com/nikon/55-200mm-vr.htm