Does your experience is about certain requirement to use F-Secure Rescue CD?
It is not possible to boot up system? Or do it safely?
Does F-Secure still supports this tool for infected Windows devices?
Probably good to know more about Windows device and type of trouble. Is it supported OS? and what is trouble there? Is it something too tricky?
Because... as it stated with one of topics - for most of common troubles - should be enough to use tools like F-Secure Online Scanner or such tools (if it is not possible to install fully bundled security solution from first).