Sure there are dll's for this, but i've once tried to make a antialiased circle, here's the sample:
Code:
Private Declare Function SetPixelV Lib "gdi32" (ByVal hdc As Long, ByVal X As Long, ByVal Y As Long, ByVal crColor As Long) As Long
Private Declare Function GetPixel Lib "gdi32" (ByVal hdc As Long, ByVal X As Long, ByVal Y As Long) As Long

Private Sub Command1_Click()
Dim dx&, dy&, X&, Y&, fade!, color1&, color2&, alpha&
     Picture = Image
    For Y = 1 To 200
        For X = 1 To 200
            dx = 100 - X
            dy = 100 - Y
            fade = Abs(100 - Sqr(dx * dx + dy * dy))
            If fade < 1 Then
                color1 = GetPixel(hdc, X, Y)
                color2 = vbRed
                alpha = RGB((color1 Mod 256) * fade + (color2 Mod 256) * (1 - fade), (Int(color1 / 256) Mod 256) * fade + (Int(color2 / 256) Mod 256) * (1 - fade), Int(color1 / 65536) * fade + Int(color2 / 65536) * (1 - fade))
                SetPixelV hdc, X, Y, alpha
            End If
        Next X
    Next Y
End Sub
Put a picture on the form and it will blend to the background.