Someone on game-deception is working on something based on this, so I shared what I did a while ago, but also posting it here for anyone interested.
The site in question is: http://www.metasploit.com/users/opcode/syscalls.html
This file is basically a C (and C++) header based on information from that webpage. It does not include all syscalls, only those that are available on all listed versions of windows. Windows 7 is not included. It contains a table of syscall numbers sorted per windows version and also function prototypes.