Hanna,
I don't think SyBase is supported for PHP4 on Win32 yet. If you need to use SyBase you'll have to either remain with PHP3, or install both 3 and 4 and then use the appropriate engine depending upon which db you're connected to. To install both 3 and 4:
You need to add in a separate ScriptAlias, AddType, and Action directive for each version of PHP to your Apache httpd.conf file. For example, you could direct Apache to send any files with the .php3 extension to the PHP3 engine while sending .php and *.phtml files to the PHP4 engine.
There is no dll for MySQL since support is built-in to the PHP4 release. Hope this helps!!
Cheers,
Geoff