setup your new user record - page not shown on windows (2/3)

I installed the standalone version on 3 windows machines, 2 vista with wamp-server and one windows server 2003,
on the first wamp I could setup the new user record, page shown correctly and processed OK,
on the 2 others the page was not shown, only the html header was send:

the only thing coming through was
"<head><style type="text/css"> body

{border: 1px #CCC solid;margin: 3em;padding: 1em 1em 1em 2em;}

</style></head>"

without error notification, nor in browser (firefox or IE), not in php or apache error log

I have no real clue what the reason is, I tried both 3.0.0 and 3.0.1, results the same, my working wamp is not the most recent one, it has:
mysql: 5.0.51b
php: 5.2.6
apache: 2.2.8

the one with the not working vista has a recent wamp installation : month september 2009.
I could do some debugging if I had a clue where to start looking..