Hi,
Assembly routines are good to work with KeilA51 compiler. U can check out the Keil.com site they have a good collection for assembly routines and good support for syntax too. And the Keypad routines u need work out an a alorithm put it into assembly make an hardware burn the hex code into the hardware and test it your self.
In Keil A51 Compiler u need to open up a new project .... select a processor ..for eg atmel family 89C51 ..then it will ask u for whether to include the source code or not ...if yes then the 89C51 initialisation code will be included in the SoureGroup1 folder beneath the Target1 folder now include ur new assembly file into the sourcegroup1 folder. AND compile your project ....bingo it will teach you everything ...after trying keep trying ..

regards
sushant