Just to mention, when upgrading mame versions, I never install into the old directory. (In fact, as far as I know, mame doesn't 'install', and has no registry interaction.) I unzip into a main directory - for me it's My Documents - and then cut or copy and paste the exe* into the old directory.
*I usually use mame32/UI, so I just do the exe. However, if I (just for testing purposes, mind) happen to grab vanilla mame, I included the other exes or whatever with it, as they're necessary for mame to run. 32/UI has them bundled together.