I have Sony Vegas Pro 10 Trail Version, and .AVI doesn't work (Though it should X.X)?

My Sony Vegas accepts .avi but I hear a lot of people have trouble with it, you can always convert the files to .mp4 Sony Vegas has no problem recognising those. The only file I know Sony doesn't accept is .MKVD I don't know about images but it accepts .jpg .png .gif. pdf so quite a few.