On of the drawbacks of google maps infowindows is that map will move to make room for the infowindow to display. ebubble( http://econym.org.uk/gmap/ebubble.html) overcomes this limitation, it doesn't move the map. However. it has its own limitations (you can't leave it on, like the infowindow, due to the way it works (it immediately hides). Also, the bubble, being absolutely positioned, might get cropped)
Are there more alternatives to the infowindow that doesn't move the map, besides ebubble?
Depending on your needs (which aren't totally clear from your description), you might consider MapTooltip, which lets you put arbitrary HTML into a tooltip. I haven't used it, but it's mentioned in this excellent presentation on Google Maps.
Alternatively, you might be able to make the InfoWindow do what you want with some event handling code. movestart and the InfoWindow's onOpenFn might let you do this - try catching movestart and remembering the map's position, then in your onOpenFn restore the position. This might look ugly, though.
If you are willing to use the Google Maps Flash API, there is a way of opening info windows without the map panning. The info window stays open until the user closes it. The user can move the map while the window remains open.
Link to example here. Right click map to view source.