Welcome aboard Peter,
If your trying to use the DX10 Preview mode of FSX simply by checking the DX10 box it will not work correctly that way there is a "fixer program" available that will make it work correctly. Somebody here will steer you to that program hopefully as I don't use DX10 Preview myself.
As for Ultimate Alaska that is not an ORBX product and I have no information as to how well it works etc. I do know that running ORBX scenery and other scenery such as UTX etc. does cause conflicts at times and most of the time there are work arounds.
RTMM scenery is designed to work within ORBX PNW, PFJ, SAK, and FSAddon's Tongass X so those are required payware plus FSX Acceleration along with the RTMM Libaries.
This is all listed on the Home Page here at RTMM and you should have those if you want to utilize RTMM scenery to the fullest.