Right, ok.
I was hoping that giving the files an extension then just associating Spinworks with that extension might help.
Also, having two different links for home and uni is absolutely fine.
I've just opened Z:\Docs\Uni\MPhil\NMR\2008-10-21-AB-26\10\fid.fid (after renaming it) from the Firefox address bar, it gives me the option to open the file with Spinworks and it works as I want it to. So that's good news. As does doing the \\server\d$\Docs\... version.
BUT...Another stumbling block will be that renaming the uni copy and giving it a file extension could be a problem and something I'd like to avoid doing