I downloaded DXTBmp.
http://www.mwgfx.co.uk/programs/dxtbmp.htm
Installed.
Dragged the texture in question (in my case, the Tristar DMTRIVC_1, _2, and TRI2/3PILOT file) into the GUI interface, one at a time. Save as Extended bmp. Select DXT3. Say yes to overwrite.
Done.
By the way, the BAC 1-11's also had a few (albeit less offending) DX10 issues - chiefly the stairs. One file per texture set (called "111STEPS), done.
It took me longer to type this than it did to do the first file conversion. It's a piece of cake. Additionally, if you set this programme as the default for opening bmps, then you can do this with ease - even if the prog isn't open, just doublclick on a .bmp to either preview it - and/or edit as required.
Thanks Dave for pointing me in the right direction - sometimes, all we need is a bit of a push.
cheers,
Daniel