I see what you're trying to do, and thanks to the fact that PC hardware
is relatively standard, you can be reasonably sure that, if you get it to
work, it will work on other machines.

Another thought, though.  If you have more lines available on the PIC end
of things, you can do other sneaky things to get data across without
disturbing the printer.

If you're willing to disable transmitting to the PIC while the printer is
actually in current use, you can use as many data lines from the printer
port as you like, and use some other line (auto-feed, printer ID,
whatever) as a strobe.  Or use D0-D6 for data, and D7 as a strobe.  As
long as you never toggle the real strobe line, the printer will ignore any
changes on the other lines.  (This approach will eliminate your precise
timing requirements, too!)

You'll probably have to invent a "magic cookie" wakeup sequence, though,
to make sure your device isn't accidentally triggered by ordinary
printouts.  I think if you use an otherwise-unused line as a strobe, or
concoct a sufficiently weird wakeup sequence, you should be fine.

David
--
Their address sums up their attitude: One Microsoft Way
        http://www.rt66.com/dthomas/