Seems you can use int 13h with function 41h, if the carry flag is not set, then the machine has the extensions.
http://home.teleport.com/~brainy/diskaccess.htm
http://www.pcguide.com/ref/hdd/bios/...ensions-c.html
But do you need a library for that? If the machine has the extionsions, you can use the machine's extensions.
