how can i create dlls for menuetos using Fasm?
is this the same as in windows (with the format "PE GUI 4.0 DLL" header) ?
Any tutorials or something?

MenuetOS has no any dynamic link libraries now. If you'll invent some good format for them - it would be great. Sorry, it's just like you can't write 'format Menuet 0.1'

There is an excellent proposal made by spideros to use OBJ files as MenuetOS dlls.

and should be enough

Yeah, I use COFF format for DLLs in C library. I just call dlopen("some.dll",RTLD_NOW); and have DLL linked into app at runtime
Converting C library to DLL is on my TODO list. I want to make dynamic loader separate app which is called by kernel and it loads app+needed libraries.
DLLs will probably contain some tiny meta info:
- dll name
- dll version
- required DLLs

Why have the dynamic loader as a separate app rather than in the kernel?

Because it's written in C. For example linux uses ld-linux.so for dynamic loading. Linux kernel itself only loads files and ELF interpreter to memory. If someone wants to port libmcoff (which is part of C library now) to MenuetOS kernel, he's welcome.