I assume by Mame 138, you are refering to the previous version of the software available
http://mamedev.org/release.html, which is currently on version 1.39?
My experience with Mame games is they tend to only work on the version of the emulator they were designed for. I have a extremely large collection that was distributed as a package with a previous version (1.3 I think). If I try and upgrade the Mame version I occasionally see a few that are broken, or slightly more buggy. I would try to get your hands on one of these collections as a stand alone unit, rather than downloading games separately. Mine is 8 DVD's I think, but it includes many of the CHD files, which are huge and take up most of 3 or 4 discs. The bulk of the games can be had on the smaller sets, that don't include the CHD. I know there are collections now with up to 12 DVD's available, 6 of which are CHD files.
As for a front end, I recall there was an XBOX Mame disc that you could get that had been ported over for PC (or the other way around). It has been a long time since I researched it though.