IMHO...
if the pocket pc's browser can view a .php page
(which i think it can..)
than you would not be having problem to code your stuff...
try to do a simple 'hello world' and see if it can be viewed in the Pocket Pc browser (if i'm not mistaken, IE right??)
if everything okay,
than most probably, there would be no problemo on your application..
and i guess, php is available in most platform.. or browser..
anyway, do tell us how it goes eh..
take care..