If you want to find-out the SID of a Domain(or local) user using powershell, here is the code.
Get the SID of domain User:
write-host (new-object System.Security.Principal.NTAccount “domainuser”).Translate([System.Security.Principal.SecurityIdentifier]) -b yellow -f red
Get the SID of local User:
write-host (new-object System.Security.Principal.NTAccount “administrator”).Translate([System.Security.Principal.SecurityIdentifier]) -b yellow -f red
If you are a programming geek and want to convert this into cmdlet(say get-sid), you can find some info here at http://www.clariusconsulting.net/blogs/pga/archive/2006/08/08/643.aspx
Happy Learning,
Sitaram Pamarthi