Apache has rewrite enabled. PHP is configured with gd2, mysql, and mcrypt. I saw a post from Sigurd saying that mbstring is not required any more. That's good, because I couldn't find a description of how to configure it. [ You might want to update your server-requirements page. ]

Although I have control of the httpd.conf file on my development machine, I don't have that control on the shared server, so I'm trying to see if I can get SilverStripe running without modifying httpd.conf, therefore no "Options ... SymLinksIfOwnerMatch" setting in the SilverStripe htdocs directory.

Installation is not at the htdocs root, it's in <htdocs>/SilverStripe/. The install script apparently doesn't remember the MySQL settings from previous runs, so I have to re-enter the password and database name every time. Also have to re-enter the SilverStripe administrator password, first and last names every time I run install.php. It seems like it should remember this stuff, but if this is normal behavior, I think it would be nice to have a note to that effect in that section of install.php.

Anyway... MySQL, php5, GD2, and XML are green; but it seems not be able to confirm that allow_call_time_pass_reference is on? It's really set to on, and I really did restart the server after enabling it. What could cause that?

In the permissions section, the webserver knows where files are stored; mysite, sapphire, cms, and jsparty folders exist, but it's unable to detect whether .htaccess, mysite/, tutorial/, and assets/ are writable. There are files in all of the aforementioned folders and .htaccess looks normal, so install was certainly able to write there and I'm not running as a different user now.

Exactly what access control is needed under Vista, for which user(s)? 'Authenticated Users', 'SYSTEM', 'Administrators', 'Users'? I don't really want to modify access control by trial and error. Would prefer to have specific recommendations.

Green after that, but I can't pull up any BlackCandy themed pages. Directing a browser to localhost/SilverStripe/ always brings up install.php, because that's where index.html redirects it to. If that's not the starting point after install, is some other start page documented somewhere? How does SilverStripe find anything but install.php?

Try to enable dev mode and you will hopefully see if there are any errors that makes it redirect to Install.php.
open mysite/_config.php and add Director::set_environment_type('dev');

I inserted the following:

Director::set_environment_type('dev');

at the top of: mysite/_config.php;

But ... nothing has changed. Do any of the following errors matter? If so, how do I get rid of them (allow_call_time_pass_reference is already enabled in php.ini)?

PHP Configuration
Check that the php.ini setting allow_call_time_pass_reference is on allow_call_time_pass_reference is set to '' in php.ini. You can install with allow_call_time_pass_reference not set, but some warnings may get displayed. For best results, turn it on.

File permissions
Is the .htaccess file writeable? Unable to detect whether I can write to files. Please ensure D:\htdocs\SilverStripe-v2.2.3/.htaccess is writable.
Is the mysite/ folder writeable? Unable to detect whether I can write to files. Please ensure D:\htdocs\SilverStripe-v2.2.3/mysite is writable.
Is the tutorial/ folder writeable? Unable to detect whether I can write to files. Please ensure D:\htdocs\SilverStripe-v2.2.3/tutorial is writable.
Is the assets/ folder writeable? Unable to detect whether I can write to files. Please ensure D:\htdocs\SilverStripe-v2.2.3/assets is writable.

Did you install its on localhost?
If yes, just forget it. Make the installation and its will be fine.
But for the allow_call_time_pass, you have to double click your wamp server, and go to php, php settings and check your allow_call_time_reference..

Yes, it's installed on localhost, but it's definitely not fine. What do you mean by 'double click' the WAMP server? The Apache 2.2 taskbar icon only offers stop, start, restart. Httpd.exe runs as a service. I opened the services applet and looked at service properties for httpd.exe, but there aren't any PHP options or a PHP tab. Not sure what you're referring to.