I've been dragging my feet replying stylz67 in the hope that some of the more knowledgeable members might drop in and rescue us.
Is there really such a thing as overkill when it comes to good flight simming??? 🙂
Man, you're soooo showing off and I envy you BUT... yes, there's always a but:
I notice that you're running FSX under Win XP and then you mention Direct X 10.
Win XP does NOT support DX10. This 'could' be the problem, so let's make sure that it isn't before we try something else. I think that you have an Option in FSX where you can disable DX10 -- those who have FSX installed will know more about this.
You know, Llain's post above yours is an interesting one and is not to be ignored. I quote from his post:
"I am runing fsx with Acceleration on Vista an 8800gt 640mb card. DX9 not DX10"
Despite his OS being Vista, his 8800Gt card doesn't support DX10 hence his reminder.
Until some more of the FSX specialists come along, you might as well read this thread: https://forum.flyawaysimulation.com/forum/topic/31845/preveiw-dx10/ it cannot harm.
"I previously downloaded from this site, FSX/FS2004 Republic F-84G Tunderjet Pack. It does an auto download, the textures files are bitmap, and it functions correctly. "
Weird, I simply don't know the answer. I'm calculating and guessing, but that won't help... Michael... where are you? 
PS: "... but makes me wonder if I'm manually dropping one wrong file somewhere? " Well, that's always a possibility but... haha.. I don't think so. Give us an example such as folder- or file name and where you're putting it.