wow! Send it along here if you can. xtomdl and makemdl are somewhat different, but there must be many similarities.
When I got FSDS 3.5.1 I was told the main upgrade was to be able to continue with aircraft designing due to some differences. If I didn't have FSX then there wasn't much reason to get 3.5.1, but I did anyway.
At the time I didn't have a tough enough machine to handle FSX. I have for years, now. ( FS9 is about 1 gig big; FSX is about 16 gigs big. )
In fsds 3.5.1 the precondition ability no longer is available. (Rats!)
To have a poly that is to be used as a transparency say- a piece of see-thru window. You make the poly then call up current item properties, go to material, add - then in the name type trans, or glass, or widow (key word either works), I use trans, the chose that so it applies to the part. THEN- apply your alpha bmp. An extra step but it's the process for xtomdl.
Another thing - In FS9 if you attach .N to yor bmp but forget to make your LM... FS9 just shows the part or object as white or black... forget which. In FSX the part renders as invisible! Found that out the hard way! hahaha I'm sure yo have heard all tis before.
of course, FS9 doesn't see dxt5, only 1 and 3. Nor does it see DDS files even though FS9 also turns bmps up side down. Weird stuff, that.
Anyway- Those files may be some help. Thanx for the idea.
Say Hi to John Stinstrom for me and some of us. I've tried to get him t come on Skype.... very much a recluse I guess!

Bob