Use Deinterlace to separate the odd and even scanlines of a clip.
To access the Deinterlace menu, use:
Timeline, then use ConnectFX (see Creating ConnectFX).
Tools, then select from the menu (See Accessing Tools).
This node accepts a front clip as input, and outputs a result.
For each frame of the clip, the result clip contains one frame with odd scanlines (Field 1) and one frame with even scanlines (Field 2).