Hit Test w/ Vector Graphics

[chainrule]

Hi, I'm writing a small drawing program in WIN32 API. I can't for the life of me find a good example of a hit test. My program zooms and pans and I use double buffing for the vectors to a bmp to the screen. So now I'm at the point where I want to code the selections of objects for transforms and drawing

I have write a couple algorithms to perform a hit test but they seem slow to me.
My app will need to support over 20,000 line/circles. Perhaps more in the future

Does anyone have any experience with this? or could point me to a sample project??? DrawCL from the Win SDK is not really what I'm looking for. I'm trying to mimic something like AutoCAD with window and crossing sections and large amounts of entities

thanks