Is the php_sybase_ct.dll you have a VC9 compile???
You should check the location you downloaded from to ascertain the version of the dll. PHP extensions have to match the compiler version used to compile Apache & PHP. XAMPP 1.7.7 for Windows is a VC9 compilation.
You might want to Google?Bing?Yahoo whatever this: "php_sybase_ct.dll vc9" to see what you come up withhttps://bugs.php.net/bug.php?id=52545
If its a VC6 compile, you would need to step back to a prior version of XAMPP that supported VC6 extensions. (I would recommend 1.7.3 for its stability)