You might that some of the articles here: http://buddhanet.net/insight.htm
which can be downloaded as PDF,
will clarify some of the instructions.
Bhikkhu Pesala's web site has many resources: http://www.aimwell.org/
He has updated up a number of translations of Mahasi Sayadaw's books and articles and he can answer questions here.
There are a number of teachers who teach variations on the Mahasi approach.
A very traditional one is here: http://dharmaseed.org/teacher/186/
And Patrick Kearney's retreat instructions, which are updated periodically here: http://dharmasalon.net/Audio/audio.html
are excellent, though I see that at the moment there is only one talk online, which is a little strange.
Steve Armstrong has some useful talks here: http://www.audiodharma.org/series/8/talk/1848/
I'd recommend starting off doing 10-15 minutes walking then 10-15 minutes sitting and work up from there.