More info:

The mod_perl and httpd tarballs were downloaded, un-gzip'd, and un-tar'd to the same parent directory. Then I did:

% perl Makefile.PL EVERTHING=1 USE_APACI=1
Will configure via APACI
Configure mod_perl with ../apache_1.3.12/src ? [y]
Shall I build httpd in ../apache_1.3.12/src for you? [y]
[download]

Much hilarity ensued. No errors. Then:

% make
# large amounts of error-free make info
% make test
# more large amount of error-free text, and then...
cp t/conf/mod_perl_srm.conf t/conf/srm.conf
../apache_1.3.12/src/httpd -f `pwd`/t/conf/httpd.conf -X -d `pwd`/t &
httpd listening on port 8529
will write error_log to: t/logs/error_log
letting apache warm up...\c
done
/usr/bin/perl t/TEST 0
still waiting for server to warm up...............not ok
server failed to start! (please examine t/logs/error_log) at t/TEST li
+ne 95.
make: *** [run_tests] Error 9
% [root@mybox mod_perl-1.24] cat t/logs/error_log
[Sat May 20 23:24:04 2000] [warn] pid file /home/builds/mod_perl-1.24/
+t/logs/httpd.
pid overwritten -- Unclean shutdown of previous Apache run?
Constant subroutine XHTML_DTD redefined at /usr/lib/perl5/5.00503/cons
+tant.pm line 175.
[notice] Destruction->DESTROY called for $global_object
[Sat May 20 23:24:06 2000] [warn] [notice] child_init for process 800,
+ report any problems to [no address given]
[download]

The "pid overwritten" message doesn't surprise me; I've been messing with this all day. It'd be a shock if there wasn't an existing pid file. But the rest of those errors confuse me.