Although an MDI application is definitely possible, the interaction between the different forms sometimes is a little cumbersome. A tabbed page is easier to handle since everything then resides within the same TForm class. If you want to change the appearance of the individual tabs you can overload the 'PageControlDrawTab' Just add an event handler, get a handle to the Canvas of the tab itself and you are free to draw is as you want. See the example below:
void __fastcall TMainForm::PageControlDrawTab(TCustomTabControl *Control,
int TabIndex, const TRect &Rect, bool Active)
{
/* OnDraw handler to change the appearance of the Tabs.
Change it to blue text on white background.
*/
String s;
TRect r;
TTabControl * tTab = (TTabControl *)Control; // Get a pointer to the tab itself
s = tTab->Tabs->Strings[TabIndex]; // Retrieve the text of this tab
Control->Canvas->Brush->Color = clWhite; // Use the Canvas to draw
Control->Canvas->Font->Color = clBlue; // .. whatever you like
Control->Canvas->FillRect(Rect);
Control->Canvas->TextRect(Rect,Rect.Left+4,Rect.Top+2,s);
}