Vegas can only see the flattened metalayer of a photoshop file so it doesn't get bogged down to a crash state like PPro2. However, the files are still big compared to a PNG file, so there's probably a lot of memory required. Jpegs probably require as much RAM memory as PNG since both have to be decompressed to work with them. So the question is, how much memory does Vegas need to display just the PSD metadata on the timeline?