Well that comment was in response to you asking about software compatibility, linney answering that anything which runs on XP will run in XP Mode, then you replying "what about things like LPT dongles?".
You may be able to get things to work by running the app's installer on Windows 7 in compatibility mode - make a shortcut to it on your desktop, then right-click the shortcut, choose 'properties' and go to the 'compatibility' tab. Select compatibility for Windows XP SP3, save it, run it and see what happens.
Alternatively, I'm not sure whether you can do this in the latest version of Windows Virtual PC but in the old version, Virtual PC 2007, you can assign a physical LPT port to a VM. If it's not possible in WVPC (I can't test as I'm not on Windows 7 here at work) then you can still install Virtual PC 2007 under Windows 7.
Nelviticus