Well, it's rather essential to know which pins are being used because different pins are mapped to different registers (i.e. different addresses). There are three 8-bit registers: data (base address), status (base address+1) and control (base address+2). The 25 pins are input, output, or bidirectional. The directionality of the data pins depends on the selected mode. For internal ports you can specify this mode using the BIOS setup, but I'm not sure how you this can be done with ports that are not integrated on the system board. The 8 data lines (which are mapped to the base register) are by default used for output only, so they won't accept any input unless you explicitly instruct the hardware to change its mode. The nice thing about the new ParallelPort object is that you can use the GUI to select input or output mode, without any further programming. There are also other advantages:
http://www.pstnet.com/support/kb.asp?TopicID=1247. If your button box is not wired to the data lines, then they are probably connected to the lines that are mapped to the status register (i.e. base address+1). I don't think you can use the ParallelPort device in this case, so you could simply fall back to the Port device.
General info about the parallel port pinning and registers:
http://en.wikipedia.org/wiki/Parallel_portInfo about using input lines with the status register:
http://pfcgroot.nl/e-prime/85-tips-and-tricks/71-button-box-on-printer-port.html