If my intention is to post on YouTube I normally render at 400x300 dpi. Pick whatever compression you like, that provides a good image with low(ish) file size (experiment here, because I generally do not use compression at all at this stage, preferring to edit the AVI in Video Impression and compress only the final output, usually with a Cinepak codec). When you upload to YouTube, it sets the dpi and compression to its own standards anyway, but if you start with a very big file it will take ages to upload, and there is a maximum size of 100MB (I think) on YouTube. Then just post the link here to the YouTube file.
