You dont need any BltBit use in GDI+ :)
All you need is to set the style in your app:
SetStyle(ControlStyles.DoubleBuffer,true);
SetStyle(ControlStyles.AllPaintingInWmPaint,true);
Then just draw like you would normally.
:)
More info here:
http://ms-help://MS.VSCC/MS.MSDNVS/cpref/html/frlrfSystemWindowsFormsControlStylesClassTopic.htm