Alright, I used svn this time to get the source and that fixed the string_256 compile errors. Now, it appears I have a linker problem with libpng:

g++ Kernel/*.o wxOil/*.o tools/*.o wxXtra/*.o --debug -L./libs/darwin -L/Users/Chris/XaraLX/wxMac-2.6.3/build-unicode-debug/lib -framework QuickTime -framework IOKit -framework Carbon -framework Cocoa -framework System -lwx_macud-2.6 -L/usr/lib -lxml2 -lz -lpthread -liconv -lm -lCDraw -o XaraLX
/usr/bin/ld: Undefined symbols:
_png_error
_png_get_io_ptr
_png_create_info_struct
_png_create_write_struct_2
_png_destroy_write_struct
_png_set_bgr
_png_set_interlace_handling
_png_set_swap
_png_set_write_fn
_png_write_end
_png_write_info
_png_write_row
_png_create_read_struct_2
_png_destroy_read_struct
_png_free
_png_get_IHDR
_png_get_PLTE
_png_get_bit_depth
_png_get_channels
_png_get_color_type
_png_get_gAMA
_png_get_interlace_type
_png_get_pHYs
_png_get_rowbytes
_png_get_sRGB
_png_get_tRNS
_png_get_valid
_png_malloc
_png_read_end
_png_read_image
_png_read_info
_png_read_update_info
_png_set_expand
_png_set_gamma
_png_set_gray_to_rgb
_png_set_invert_alpha
_png_set_read_fn
_png_set_read_status_fn
_png_set_sig_bytes
_png_set_strip_16
collect2: ld returned 1 exit status
make[1]: *** [XaraLX] Error 1
make: *** [all-recursive] Error 1

I downloaded and compiled libpng 1.2.10, but maybe the linker isn't seeing it?