OK, after some test I got a solution :).
A fairly simple solution.
It looks like AOLServer ignores the parameters in the query string if the method used was POST, but even then it is possible to obtain the query string using.
set query [ns_conn query]
and then parse it with:
set get_variables_set [ns_parsequery $query]
and finally we can get the variables value using the resulting ns_set
set getvar [ns_set get $get_variables_set "getvar"]
:D
