Hi stoffel,
Yeah, shouldn't be a problem. I just tried avx005.asm (from the "test" directory in the source code) on my clunky old P4 with nasm-2.09.10 and it seemed to go okay. I can't test the result, of course!
Nasm's "cpu" directive disables instructions "higher" than the specified cpu (causes an error). Without a "cpu" directive, or any other special flag, Nasm should assemble "anything". You'll want a fairly recent version of Nasm, to get "bug free" (we hope) avx instructions.
Try it, and let us know if you encounter any problem.
Best,
Frank