It appears that a recent change (on or after Nov 2) has broken the  
build on my OS X 10.3.9 system:

gcc -fpascal-strings -DMAC_OSX -I../mac/src -DHAVE_CONFIG_H -I. -I../ 
src -I/Users/dr/Aquamacs/emacs/lib-src -I/Users/dr/Aquamacs/emacs/lib- 
src/../src  -fpascal-strings -DMAC_OSX -I../mac/src   -g -O2  /Users/ 
dr/Aquamacs/emacs/lib-src/emacsclient.c getopt.o getopt1.o - 
DVERSION="\"22.0.90\""  -o emacsclient
In file included from /Users/dr/Aquamacs/emacs/lib-src/emacsclient.c:45:
/usr/include/netinet/in.h:255: error: parse error before "in_addr_t"

full log here: http://homepages.inf.ed.ac.uk/dreitter/Aquamacs/emacs- 
build.log

It appears that this doesn't occur on more current OS X versions  
because they include this in their netinet/in.h:

----
#include <sys/_types.h>

#ifndef _IN_ADDR_T
#define _IN_ADDR_T
typedef	__uint32_t	in_addr_t;	/* base type for internet address */
#endif

#ifndef _IN_PORT_T
#define _IN_PORT_T
typedef	__uint16_t	in_port_t;
#endif
-----

which is not present in the 10.3.9 variant.

A recent revision is likely to be responsible:

revision 1.83
date: 2006-11-02 09:54:09 +0000;  author: lektu;  state: Exp;  lines:  
+7 -22
[WINDOWSNT]: Define HAVE_INET_SOCKETS.
[!WINDOWSNT]: Include <netinet/in.h> if available.
[HAVE_SOCKETS]: Also require HAVE_INET_SOCKETS.
(IOCTL, IOCTL_BOOL_ARG): Remove.
(set_tcp_socket): Don't set the socket in blocking mode.  Remove c_arg.


Hope that is specific enough.