Hi frax,
this might be a solution for your problem:
1) Download and install the powerful freeware autoit3 (
http://www.autoitscript.com/autoit3). This will do no harm to your system. The extension .au3 will be associated with autoit afterwards.
If you don't want to install the whole package: The only file you really need is the file autoit3.exe, but you should associate .au3-files with autoit for easier handling.
2) Create a text file with the extension ".au3" in a directory of your choice, e.g. "d:\data files\dospath.au3". The content of this file is only a single line:
3) In Salamander, create a new user menu entry and name it e. g. "DOSPath". Provide the following details:
Command: d:\data files\dospath.au3
Arguments: $(DOSFullName)
Initial Directory: $(FullPath)
Uncheck "Execute through shell"
Choose an icon of your liking. Make sure that the option "Show item in User Menu Bar" is checked. Of course the user menu toolbar must be visible.
4) Now, when you click on the icon in the user menu bar, the DOS 8+3 path and name of the highlighted file will be copied to the clipboard (without the trailing space you get with Jan's workaround)