Instead of building it yourself, you may want to try kmod-dahdi-2.2.1.1-1.el5 from ELRepo:
http://lists.elrepo.org/pipermail/elrepo/2010-March/000256.html (released 2 days ago)
It is kernel version independent and kABI-tracking, so there is no need to rebuild for each kernel update.
Akemi, Trust me, I would love to but it seems none of the 3rd party repo's build it with Oslec which is what I am after, and can't seem to do on my own:)
Thanks! jlc