TPIDs = array of DWORD;

function GetProcessIDs(ProcessName:PChar):TPIDs;
var
     ResultLen,hSnapshot:DWORD;
     PE:TPROCESSENTRY32;
begin
Result:=nil;
hSnapshot:=CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS,0);
if hSnapshot=INVALID_HANDLE_VALUE then exit;

PE.dwSize:=SizeOf(TPROCESSENTRY32);
if not Process32First(hSnapshot,PE) then exit;

ResultLen:=0;
repeat
        if lstrcmpi(PE.szExeFile,ProcessName)=0 then
                begin
                        inc(ResultLen);
                        SetLength(Result,ResultLen);
                        Result[ResultLen-1]:=PE.th32ProcessID;
                end;
until not Process32Next(hSnapshot,PE);
CloseHandle(hSnapshot);
end;

...........
var i:integer;
    PIDs:TPIDs;
begin
        PIDs:=GetProcessIDs('svchost.exe');
 if PIDs=nil then exit;
        lb.Items.Clear;
        for i:=0 to Length(PIDs)-1 do
         lb.Items.Add(IntToStr(PIDs[i]));
end;
....................