Are there instructions for using the Twokp program?  I downloaded all
> the files from the /Mersenneplustwo/Binaries/Twokp/cygwin folder.  I am
> running Win XP with SP2, so I added an etc folder to my root directory.
> I created a test.txt file with 2 numbers in it and opened a command
> prompt and entered the following: twokp < test.txt
> It seems to run OK, but I am not sure what it is doing.  Are the
> number(s) in the test.txt file the p value of 2^p+1?  Does p need to be
> a prime or will it find factors of 2^n+1 with n a composite?
>

You need to feed it a pair of numbers, separated by one (or possibly
two) <RETURN>s.
The first number is the p value (as you surmise) - it should also do composites.
Then after (probably) two <RETURN>s it should echo the value of 2^p+1.
Then you provide it with a start point ie starting index, which is
equal to k, when testing divisors starting at 2kp+1.
After another two <RETURN>s it starts to calculate, showing any
factors, and the value of k tested up to. [so you can restart at this
new k next time]

Though I ought to just mention (having only just tried it myself!)
that the behaviour for p composite may not be entirely
comprehensive/expected/predictable - the program was only designed for
p prime (and Mersenne prime at that), after all :-)
[to be more specific, the program _strictly_ and simply looks for
factors of the form 2kp+1 - if p is a composite the math says that
there may be factors of 2^p+1 which are _not_ of this form, and hence
will be missed]

Please also note that for larger exponents you should use Primemx2, as this will be significantly quicker.