VGA vs Mini-DVI to HDMI adapter

Well dvi is an hd quality signal so you should get the best quality that your MacBook is able to output through the cable, seeing as youre going from an inferior technology to a superior one you shouldnt loose quality, if the scenerio were the other way around it may be a different story however. the big advantage HDMI had over DVI was that it carried audio signal along with HD signal. So you will lose audio but on the video front you should be fine.

I don't really know how to answer the second part of your question, if you really need it then, yes, I would buy it. You can find them, on the web for like $7.

If your macbook has mini-DVI then HDMI or no HDMI you will not get any audio passed through the HDMI connection because DVI does not pass audio. You would need to pass the audio separately via analog stereo line out.

But what difference does it make anyhow? You intend to use this as a monitor as opposed to hooking it up to a HDTV.

So long as you use a digitial interface HDMI, DVI, mini-displayport, etc. you are not going to loose any quality. It's digital. It either works or it doesn't. VGA, being analog, will of course be less quality.

I don't even know why you care about converting to HDMI when you could just convert mini-DVI to standard DVI and use a monitor that accepts standard DVI. They're plenty of those around.

Another consideration with a DVI interface is that if the monitor has a resolution greater than 1920 x 1200 you need a dual link DVI adapter as opposed to a single link DVI adapter.