Thanks for all the information you have provided. It is remarkable how much time and energy people put into providing such details to the community. You should probably check your fourth overlay. I was able to download and install the first three but the fourth (for downtown) gives a 404 not found error.

I also face the frustration that the overlay for the City Map is too large for my modest 64 MB nVidia card (Ti4200 GeForce 4) so it shows up all black. When I finally pop for a new card (halflife 2 is not as smooth in some parts as my children would prefer) I will have the overlay in place and ready to view. I'd like to visit Budapest someday and your guide should prove useful.