I just installed WAMP and found the same problem, but I was able to solve it as follows:
On the WAMP menu (accessed from the system tray), expand php settings, then expand php extensions (the folder at the bottom of php settings) , and scroll for awhile until you see php_xsl, then click that to enable it.
If you close the menu, then expand and scroll to php_xsl, you will see it has a check mark next to it now.
After doing that I tested my transformation and it worked!