Thanks ferday for pointing me in the right direction. What I ended up with is:
=removeleft(filefolder([filename,0],0),3) - removeleft(filename([filename,0],0),5)
For the benefit of anyone else wanting to do something similar:
[filename,0] simply references the name and path of the file.
e.g. "D:\Training\Course Name\02.Chapter Name\0102.Filename.wmv"
The filefolder() function
http://wiki.jriver.com/index.php/FileFolder()#FileFolder retrieve the part of the path specified but numbers from right to left so 0 is the folder containing the file and higher numbers specify folders closer to the root of the drive.
In my example "02.Chapter Name"
The filename() function
http://wiki.jriver.com/index.php/FileFolder()#FileName retrieves the name of the file with the option 0 discarding the file suffix.
In my example "0102.Filename"
N.B. filename() is a function and different from [filename,0] which references a field.
The removeleft() function
http://wiki.jriver.com/index.php/RemoveLeft()#RemoveLeft removes a specific number of characters from the string so I could get rid of the preceding numbers in my file path.
The first one removes 3 characters leaving me "Chapter Name" and the second 5 leaving me "Filename"
Putting it all together give me "Chapter Name - Filename"
I then selected all the files I want to edit and using the tag editor pasted my expression into the name tag and hey presto all my tags are updated.
Thanks again