When moving the following script from PHP on Win32 to PHP on Linux, I encountered problems:

$c = mssql_connect("SERVER∖INSTANCE","UID","PWD");

After much searching, I discovered that 'instances' are just named aliases for port numbers, so on Linux this should be written:

$c = mssql_connect("SERVER:PORT","UID","PWD");

Please also note that the colon (:) should be used on Linux as the delimiter between servername and port number, not the comma (,) which only works on Win32 servers.