Janus. I'd also like to suggest the use of a skip table that specifies how many frames to skip before acquiring an image. This way your Vision hardware stays in sync with the camera, but just skips a specified number of v-sync signals before actually acquiring image data. This way you can avoid Windows based Timers or loop delays, and still acquire at a lower frame rate.
There is an example that ships with LabVIEW called HL Sequence in IMAQ Vision display.vi, and is located in the IMAQ High Level.llb. It can be modified with a loop to run continuously.