I've done it several times. Works pretty well. Some programs may need to be reinstalled, some re-tweaked. It's not perfect, but every time I've done it XP will boot and the PC will run. Just a few little annoyances, but it beats having to do a full format and reinstall everything.
Has anyone successfully used the maxblast 4 tool to move os to new drive from old. Old drive is western digital. Don't have to. Considering.