Hey! Looks like you're a new member, so welcome! This sounds like a really interesting. I've been looking into this myself, so maybe I can help out. If you don't need the functionality of google maps, you could try doing something with Flash, or layered images on a webpage. It would also help to have a vector map of the world, rather than a raster image, so you can build the map and then zoom in and out without losing the clean lines. I guess a couple questions:
1) How many "zoom levels" are you interested in? do you want to be able to zoom in to see individual buildings, like google "map" view? Or do you just want to zoom in far enough to see most streets (like google "map + terrain" view?
2) Do you have a whole planet you're "working down from", or do you have various areas/regions that you'd want to have zoomable maps for, and then you'd add to those?
3) How big is/are the area(s) you want mapped for zooming?
4) Not entirely relevant, but is this a more "low fantasy"/"medieval" style map/world, or are you doing something more modern? This more affects the "look" of the maps themselves, really.
I'm working on some stylized maps right now, but I can also create vector maps and I sort of know Flash, so if you need any help with this, let me know. I'd love to help. Good luck! ^-^