Here's what I have so far to get the SID from a specific account.

FUNCTION GetSid
* Retourne le SID
* expC1 Nom du serveur
* expC2 Code d'usager
PARAMETER tcServer,tcUsername
DECLARE INTEGER LookupAccountName IN WIN32API;
STRING @,STRING @,STRING,INTEGER @,STRING @,INTEGER @,INTEGER
LOCAL lcSID,lcDomain
lcSID=SPACE(255)
lcDomain=SPACE(255)
tcServer=tcServer+CHR(0)
tcUsername=tcUsername+CHR(0)
? LookupAccountName(@tcServer,@tcUsername,@lcSID,255,@lcDomain,255,1)
? lcSID
? lcDomain

This is giving me a Dr. Watson free visit. If someone can detect what is wrong, I will appreciate that. :)