Is the IM driver liable to break in Vista whenever MS patches the OS?
As far as I know IM drivers were not declared depreciated in Vista, so probably they won’t be unexpectedly dropped in one of the forthcoming SPs.
Will Vista support be upgraded to use the native Windows Filtering Platform or do you have a timetable when that might be rolled in?
WPF is relatively new and I would refrain from using it until Vista finally released along with final new WDK. The only WPF sample from beta WDK I seen so far was not able to send requests (NdisRequest) to the underlying NDIS miniports. May be it will be fixed (or even already fixed) but in the meantime it is a serious limitation.