const
basetzikey = 'SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones\';

procedure TWinForm.FillComboBox(cbxCombo: ComboBox);
var
rootkey: RegistryKey; //Microsoft.Win32.RegistryKey
subkeynames: array of string;
subkeyname: string;
begin
cbxCombo.Items.Clear;
rootkey:= Registry.LocalMachine;
subkeynames:= rootkey.OpenSubKey(basetzikey,false).GetSubKeyNames;
for subkeyname in subkeynames do
cbxCombo.Items.Add(subkeyname.ToString);
end;

procedure TWinForm.FillTextEdit(timezone: string; txtEdit: TextBox);
type
bytearray= array[] of byte;
var
sb: System.Text.StringBuilder;
rootkey: RegistryKey; //Microsoft.Win32.RegistryKey
subkeyvalues: array of string;
subkeyvalue: string;
keyname: string;
b: bytearray;
i: Smallint;

begin
txtEdit.Clear;

sb:= StringBuilder.Create;
sb.Append(basetzikey);
sb.Append(timezone);
keyname:= sb.ToString;

sb.Remove(0, sb.Length);

rootkey:= Registry.LocalMachine;
subkeyvalues:= rootkey.OpenSubKey(keyname,false).GetValueNames;
for subkeyvalue in subkeyvalues do
begin
sb.Remove(0, sb.Length);
sb.Append(subkeyvalue);
sb.Append(': ');
sb.Append(rootkey.OpenSubKey(keyname,false).GetValue(subkeyvalue).ToString);
sb.Append(#13#10);
if subkeyvalue = 'TZI' then
begin
// you could reporduce the TIME_ZONE_INFORMATION record
// I am just looking for the BIAS which is the first two bytes
// of the structure
b:= bytearray(rootkey.OpenSubKey(keyname,false).GetValue(subkeyvalue));// as bytearray;
i:= b[1] shl 8;
i:= i + b[0];
sb.Append('Bias: ' );
sb.Append(i);
sb.Append(' minutes.');
sb.Append(#13#10);
end;
txtedit.AppendText(sb.ToString);
end;
end;

procedure TWinForm.cbxTimeZone_SelectedIndexChanged(sender: System.Object; e: System.EventArgs);
begin
FillTextEdit(ComboBox(sender).Text,txtOutput);
end;

constructor TWinForm.Create;
begin
inherited Create;
InitializeComponent;
FillComboBox(cbxTimeZone);
end;