I read your post, and I found the solution to the problem in about two seconds by doing a web search for "apache auth nt". Aparently that's not "easy" enough for you though so I will give you some pointers:
here is an NT auth module for apache
http://www.ozemail.com.au/~timcostello/mod_ntlm/
other interesting links in the same set of search results...
here is a page on a mysql module for apache:
ftp://ftp.kcilink.com/pub/mod_auth_mysql.c
here is some info on PAM which supports MANY auth types:
http://www.kernel.org/pub/linux/libs/pam/modules.html
and the apache module for pam:
http://blank.pages.de/pam/
See.. not so hard after all if you just bother to look.