Use win98se and xp.
Best of both worlds.
Multi partition your HD and use a bootmanager. That way you can have two primary partitions (obviously only one active at once).
If you want to go all the way, you can have a separate data partition and a separate appz partition that can be seen by either OS.
Image each partition and the common data partition, that way if one ever crashes you can switch in one reboot, or reimage in less than 10 mins.
Also, all your data, mail, bookmarks etc are all common to one OS.
It takes a little longer to setup, but it's well worth the effort.
Santa