3. If you want a good reliable and fast OS stick with 2K and leave XP alone. XP is just an ugly (IMHO) new face for the 2K.
Windows XP also uses prefetching when launching applications. The files and the contents of the files accessed by each new process are observed and recorded. No prefetching can be done for the first launch of an application, so first launches are often considerably slower than subsequent launches. About 85% to 90% of the improvement is realized after just one launch of an application, with the remaining speed improvement coming after the system has had an opportunity to adjust the disk layout with information specific to this application.