Thanks for the helpful advice. To close out this thread, here's what I've learned over the past few days.
1. Currently there is a problem trying to install mySQL and some of the Perl modules on a 64-bit Mac running 10.5.x. In particular, installing via CPAN is unlikely to work as one needs to use configuration flags such as
-CFLAGS="-arch x86_64 "
as part of the "./configure" or "Makefile.PL" command.
Also, the current 64-bit version of mySQL for (Mac) Leopard 10.5.2 has a bug working with the Preference panel included in the binary package. I had to make a clean reinstall.
2. For packages such as Apache2::Request and DBD::mysql, for which a CPAN installation gives errors, one needs to do a manual install. For me, it was easiest to download the .tar.gz file, and then run
./configure or Makefile.PL
make test or make check (optional)
sudo make install
For some packages, one needs to run sudo make or sudo make test as they require permissions. But for other packages, (such as Apache::Request) you don't want to run "make test" as the superuser.
3. In the end, the order of installation was mysql, Apache2, mod_perl2, Apache::Request, DBD::mysql, but I'm not sure the order of the last three mattered. It's just they increased in difficulty in the number of flags they used, so starting with the easier installations is probably best (since I learned what I was doing as I went).
4. I would recommend not using Fink currently for installations on a 64-bit Leopard platform. In the end, I had to delete most of the programs and libraries I installed using Fink as they seemed to be 32-bit based. The manual installations (once I knew what I was doing) worked much better.