Decimal output is easy...with printf.

Use the Microsoft Visual C Runtime (msvcrt.dll, libmsvcrt in GCC's case) to allow for the printf function (_printf in Windows-speak). For unsigned values, use the "%u" format specifier and for signed values use one of the "%d" or "%i" format specifiers:

; nasm -f win32 -o blah.o blah.asm
; ld -o blah.exe blah.o -lmsvcrt
section .data
val equ 0xffffffff
TAB equ 0x09
LF equ 0x0A
s_printf: db "Signed (ASCII):", TAB, TAB, "%i", LF, 0
u_printf: db "Unsigned (ASCII):", TAB, "%u", LF, 0
s_wprintf: dw "S", "i", "g", "n", "e", "d", " ", "(", "w", "i", "d", "e", ")", ":", TAB, TAB, "%", "i", LF, 0
u_wprintf: dw "U", "n", "s", "i", "g", "n", "e", "d", " ", "(", "w", "i", "d", "e", ")", ":", TAB, "%", "u", LF, 0

section .text
extern _printf ;for ASCII characters
extern _wprintf ;for "wide" characters
global _main

_main:
push ebp
mov ebp, esp

push dword val
push dword s_printf
call _printf

push dword val
push dword u_printf
call _printf

push dword val
push dword s_wprintf
call _wprintf

push dword val
push dword u_wprintf
call _wprintf

leave
xor eax, eax
ret
;;;;;;end

If it doesn't work, feel free to say so. I tested it using Wine in Linux, not Windows. :P