Can I attach an Mac mini to a VGA monitor using an HDMI/VGA adapter?
Does the adapter work with other devices? If not, then your adapter is likely broken. You should be able to attach an HDMI to VGA adapter to your Mac. Video adapters aren't computer/software specific. Side note, it would be a better idea to convert HDMI to DVI instead of VGA since HDMI and DVI are both digital, meaning they will output higher quality video, whereas VGA is analog, and will output lower quality video.