> I added the ScriptAlias and Alias directives to apache2.conf AFTER
> installing GSDL and building the collection.

Silly question but did you remember to tell apache to load the
new configuration after editing its config files? You have to do

/etc/init.d/apache2 reload

for it to pick up changes in config files.
(ps - it's always a good idea to run 'apache2ctl configtest' first so
apache will tell you if you have any typos in your config files before
you do a reload or restart).

John