DAHDI drvers & tools form the new version of ZAPTEL driver.
You can use either DAHDI or ZAPTEL with Asterisk 1.4.22 but the DAHDI version is newer and should be your preference for any new installation or major upgrade. You CANNOT install both on the same server, that path leads to much stress and many wasted hours.
The change was only in name really and was meant to be a smooth transition. I believe that FreePBX 2.5.1.0 understands either of the drivers but I have no experience as my systems don’t use that.
Oh, and if you have installed ZAPTEL then you go to DAHDI make certain that ZAPTEL didn’t leave modules behind as they clash with the new modules.