To remove user from Group

Question

I created a new user account from SSH connection to our cluster. The user belongs to two groups by default: nobody and wheel. I tried to delete him from the two group by using dscl command, I got the following error:
/NetInfo/root/Groups > delete wheel GroupMembership ryan
<main> attribute status: eDSAttributeNotFound
/NetInfo/root/Groups > read wheel
AppleMetaNodeLocation: /NetInfo/root
GeneratedUID: ABCDEFAB-CDEF-......
GroupMembership: root
Password: *
PrimaryGroupID: 0
RealName: System Group
RecordName: wheel
RecordType: dsRecTypeStandard:Groups
SMBSID: ......
I would like to know how to remove him from the two groups. Thank you very much.
Apple Cluster   Mac OS X (10.4.3)  

Answer 1

I had to update the code to the following because Get-SPUser was not working properly:
$url = "https://sharepointdev.spfarm.spcorp.com/sites/desitecoll"
$userName = "spfarm\spprofileimport";
$site = New-Object Microsoft.SharePoint.SPSite($url)
$web = $site.OpenWeb()
$siteGroups = $web.Groups;
Clear-Host
$mySiteGroups = @();
foreach($group in $siteGroups)
Write-Host $group
$mySiteGroups += $group;
}#foreach
$members = $web.Groups[$mySiteGroups[0]];
$owners = $web.Groups[$mySiteGroups[1]];
$visitors = $web.Groups[$mySiteGroups[2]];
#Convert the user name to an SPUser account
$spUser = $web.Site.RootWeb.EnsureUser($userName);
Write-Host $spUser.ID
Remove-SPUser -Identity $spUser -Web $url -Group $owners
$web.Update();
$web.Dispose();
Write-Host "User " $userName "removed from " $owners
Was I not using Get-SPUser correctly?