Windows, DLLs and php.ini

I've looked at the documentation but was able to find this. If anyone can point me to the right page, it would be much appreciated. In any case, where do you define where PHP looks for the appropriate DLLs? For example, if a DLL (say, ntwdblib.dll) is in both the "\PHP\dll" directory and the "\windows\system32" directory, which does PHP pull in? And where do you specify which directory is used? Additionally, where can you find detailed information about what the mssql configuration options actually do? IE, mssql.textlimit, mssql.max_persistent, mssql.timeout, et. al. thnx, Chris