Run MAME32 from the CD and go to Options - Default Game Options - Controllers - and look at the drop-down box for Default Input layer. You should be able to scroll down and select X-Arcade (but you said custom front-end - so this may be disabled, in which case it's tough to help you).
However, you will probably have to manually select this every time you start MAME32 if you are running off the CD.
I highly recommend copying the entire CD to a C:\MAME32 folder, and then highlighting all the files, right-clicking and unchecking "Read-Only" on the properties tab, and then running MAME32 from there.