Unable to load dynamic libraries - Win XP/Apache 2/PHP 4.3

So a forced reinstall on my computer has me putting PHP, Apache, and MSSQL
back together. PHP (4.3.9) and apache (2.0.something) seem to be talking to
each other, but they can't seem to find my extensions. I get this error
message when I start up Apache:

Unknown(): Unable to load dynamic library 'C:/php/extensions/php_mssql.dll'-
The specified module could not be found

I also get the same message for the gd2 dll.

This is somewhat mysterious, considering if I look in C:\php\extensions,
both dlls are in fact there.

In my php.ini, I have:

extension_dir = "C:/php/extensions/"

which seems to be taking effect, given that the error message gives the
pathname, but obviously it isn't finding the dll.  (I've  also tried setting
it with falling slashes, ie \'s)

Any ideas on what else to try?

-Weston