I realized I should probably submit a patch that worked.. 
it works with 4.0.6, but not 4.0.7dev. The tests that 
configure (4.0.7dev) runs to check for SSL support in 
c-client misidentifies the krb4 c-client as having ssl.   I 
can configure and build 4.0.7dev if I disable the 
IMAP_CHK_SSL in ext/imap/config.m4 and rerun buildconf.

configure: error: This c-client library is build with SSL 
support. 
      
      Add --with-imap-ssl<=DIR> to your configure line. 

Check config.log for details.
config.log:
configure:25058: gcc -o conftest -g -O2  
-D_POSIX_PTHREAD_SEMANTICS  -R/usr/ucblib -L/usr/ucblib 
-R/usr/local/gnu/lib/gcc-lib/sparc-sun-solaris2.6/2.95.2 
-L/usr/local/gnu/lib/gcc-lib/sparc-sun-solaris2.6/2.95.2 
-R/usr/local/build/imap-2000c/lib 
-L/usr/local/build/imap-2000c/lib -R/usr/local/krb4/lib 
-L/usr/local/krb4/lib conftest.c -lcrypt -lpam -lcrypt 
-lresolv -lresolv -lm -ldl -lnsl -lsocket  -lsocket -lgcc 
-lcrypt -ldes -lkrb -L/usr/local/build/imap-2000c/lib 
-lc-client 1>&5
Undefined                       first referenced
 symbol                             in file
tkt_string                          
/usr/local/build/imap-2000c/lib/libc-client.a(osdep.o)
(bunch of these for the krb4 functions).  I think it's 
because it's put an -lcrypt where it doesn't belong and 
it's conflicting with some of the calls in the krb4 des 
library.  Not sure tho..

So.. here's the patch for 4.0.6.. again, it works as a cgi, 
but not as an apache server module, and i've no idea why. 
Trying to figure that part out..

diff -p -N -U 4 -r ext/imap/config.m4 
ext/imap.krb4/config.m4
--- ext/imap/config.m4  Mon May 21 20:38:46 2001
+++ ext/imap.krb4/config.m4     Tue Aug 21 16:03:59 2001
@@ -20,8 +20,25 @@ AC_DEFUN(IMAP_LIB_CHK,[
     fi
   done
 ])
 
+AC_DEFUN(PHP_IMAP_KRB4_CHK, [
+  PHP_ARG_WITH(krb4,for KerberosIV support in IMAP,
+  [  --with-krb4[=DIR]     IMAP: Include KerberosIV 
support.])
+
+  if test "$PHP_KRB4" = "yes"; then
+    test -d /usr/kerberos && PHP_KRB4=/usr/kerberos
+  fi
+
+  if test "$PHP_KRB4" != "no"; then
+    AC_DEFINE(HAVE_IMAP_KRB4,1,[ ])
+    PHP_ADD_LIBPATH($PHP_KRB4/lib, IMAP_SHARED_LIBADD)
+    PHP_ADD_LIBRARY(des, 1, IMAP_SHARED_LIBADD)
+    PHP_ADD_LIBRARY(krb, 1, IMAP_SHARED_LIBADD)
+  fi
+])
+
+
 AC_DEFUN(PHP_IMAP_KRB_CHK, [
   PHP_ARG_WITH(kerberos,for Kerberos support in IMAP,
   [  --with-kerberos[=DIR]     IMAP: Include Kerberos 
support.])
 
@@ -134,7 +151,8 @@ if test "$PHP_IMAP" != "no"; then  
 
     PHP_ADD_INCLUDE($IMAP_INC_DIR)
     PHP_ADD_LIBPATH($IMAP_LIBDIR, IMAP_SHARED_LIBADD)
     PHP_ADD_LIBRARY_DEFER($IMAP_LIB)
+    PHP_IMAP_KRB4_CHK
     PHP_IMAP_KRB_CHK
     PHP_IMAP_SSL_CHK
 fi
diff -p -N -U 4 -r ext/imap/php_imap.c 
ext/imap.krb4/php_imap.c
--- ext/imap/php_imap.c Tue Aug 21 16:06:23 2001
+++ ext/imap.krb4/php_imap.c    Tue Aug 21 16:44:31 2001
@@ -449,8 +449,9 @@ PHP_MINIT_FUNCTION(imap)
 #ifndef PHP_WIN32
        mail_link(&mmdfdriver);         /* link in the mmdf 
driver */
        mail_link(&newsdriver);         /* link in the news 
driver */
        mail_link(&philedriver);        /* link in the 
phile driver */
+       auth_link(&auth_krb);           /* link in the krb 
authenticator */
        auth_link(&auth_log);           /* link in the log 
authenticator */
        auth_link(&auth_md5);       /* link in the cram-md5 
authenticator */ 
 #ifdef  HAVE_IMAP_SSL
        ssl_onceonlyinit ();

Before anybody commits this patch here's a note from IMAP 
docs/FAQ:
----------------------------------------------------------
Q: Can I use Kerberos V4?
A: Kerberos V4 is not supported.  Kerberos V4 client-only contributed code
    is available as:
     ftp://ftp.cac.washington.edu/mail/kerberos4-patches.tar.Z
   This is a patchkit which must be applied to the IMAP toolkit according
    to the instructions in the patchkit's README.  I can not promise that
    this code works.
----------------------------------------------------------

And we're not going to add anything that isn't supported
by the c-client library.