You can google for "dds converter" - there are some programs.
But you have to be carful - convert the textures one by one and make a backup in advance. I am not sure if it works with all the textures. I had some problems with some textures.
Thank you Manuel, I will look into this. I have installed the Tu-114 in FSX Gold Edition (I am a Xmas newb). Most of it works except for the flight deck and passenger cabin textures. When vc is selected, the base textures appear for a moment then disapear. The panel instruments are visible and working. The control yoke is not visible but it works (it's transparent "shadow" blocks the instruments behind it).
In the passenger cabin, only the overhead storage netting is visible.
On the positive side, the aircraft is flyable and pilot visibility is outstanding.