You can use long filenames in DOS 7+ as long as you run a TSR that provides the functionality. I have use LFNDOS in the past but there is also DOSLFN and others. In MS-DOS version 6.22 and below the commandline doesn't support long filenames even if a driver supporting the API is installed, but programs that take advantage of it will work as expected, e.g. an ACE archiver by Marcel Lemke IIRC. Programs that do not handle long filenames in Windows will not magically gain the ability since they will still use the older 8.3-style API. There are also non-TSR programs that are designed to replace the functionality of the internal DOS commands.

http://sta.c64.org/lfnemu.html
http://home.att.net/~short.stop/freesoft/windos.htm
http://www.geocities.com/jadoxa/ The fourth entry is DOSLFN.