Hi there
Just wondering whats the best way to get frame grabs from HV20 video. Also would it be best to shoot 24p or 60i. Please help I have no idea how to do this. Thanks

In Vegas, set your preview window to Best full resoluition, that then press the "disk" icon at top of window, and follow prompts to name saved file.

Other editors have similar features.

When I try this I get 'lines' on snapshots from moving images (working from 60i images). What to do?

you can get good frame grabs from the HV20, but you really need Photoshop to do it, first because if you are shooting 60i, you need to apply the de-interlace filter, a must with 60i images, those distracting lines that you are seeing are the interlacing. but also you need to resize the image from 1440 to 1920...

you can set up an action to automate these two functions in Photoshop, if you have a lot of stills, you can add the action and it will do the work very fast. there are probably other pathways to do this, re-size and de-interlace, besides using Photoshop, but you won't get good stills in 60i unless you do both those things.