Vista - a set-acl (change owner) problem

Hi guys.

I'm trying to set-up a virtual web folder and to do it I firstly
create it then (trying to) set owner to the user i create it for and
finally mark it a virtual web directory.

Here how it goes:
write-host -n "nazwa konta:"
$username = Read-Host
if( $username.trim() -eq "")
{ break; }


### tworzymy strone

$homedir = (ls env:homedrive).value + "\Documents and Settings\" +
$username + "\My Documents\"
$wwwdir = $homedir + "public_www"
mkdir $wwwdir


$account = new-object system.security.principal.ntaccount("CHESLAV\" +
$username)
$acl = get-acl -path "$wwwdir"

$acl.setowner($account)
set-acl -path "$wwwdir" -aclObject $acl #### here i get the error
cacls "$wwwdir" /E /G IUSR_CHESLAV:R > $null

iisvdir /create "Uzytkownicy" "$username" "$wwwdir"


Unfortunately, get the error saying:
Set-Acl : The security identifier is not allowed to be the owner of
this object.
At line:1 char:8
+ set-acl <<<< -path "$wwwdir" -aclObject $acl

and if I try to use xxx instead i receive the following:
PS C:\root> $dirobj.setaccesscontrol($acl)
Exception calling "SetAccessControl" with "1" argument(s): "The
security identifier is not allowed to be the owner of t
his object."
At line:1 char:25
+ $dirobj.setaccesscontrol( <<<< $acl)
(where $dirobj is retrived using get-item $wwwdir in this case)

What's worth a notice, when $account is acquired frome
"Administrator", all goes well.

Any help?