Hi Bob,
I'll answer each one in turn.
1. It's possible that switching will resolve the problem as you will be using a new database and server files, but you ideally need to identify the root problem with your vB installation to ensure it is not server or host related. It's possible that your vB installation has been compromised and some malicious code inserted somewhere.
2. As per 1, I don't think the problem will exist in XenForo if it is related to your vB installation.
3. a vB4 importer is available here - members, forums, threads, posts and attachments will all be imported but please note the limitations: http://xenforo.com/community/threads/vbulletin-4-importer.5726/
4. Yes.
5. Official ticket support is available but most people get support on the forums.
Oh and yes, I can rebuild a 1958 Chevy carb' 
Hope that helps.
Any other questions, feel free to ask.
