Illustrator won't help. A path in Photoshop, a line that you draw with the pen tool, doesn't really have a corollary in Flash. In Flash the pen tool draws a line. The operation of the pen tool is very similar to Photoshop, but the output is treated differently.
A guide in Flash is usually a line of some sort that has a beginning and an end. So a circle won't really work as a guide line because it has no ends. If you erase a part of the line, then it will work.
So, if your existing path from Photoshop is a continuous shape, you'll have to cut out a small section.
Does that help to explain the path in Flash?