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Besides the loss of restore points you can also elect to back up the entire registry in one file by this guide.
Registry - Backup and Restore
Hiding the Vista or 7 primary from XP was the main method used since this was first seen as a problem with the previous version when dual booting. Once the newer version's partition was hidden from XP the restore points made by the newer version were uneffected when booting into the older XP.
In order to protect the Vista restore points from an XP/Vista dual boot a new utility project was started but abandoned for actually seeing the Vista primary hidden and the restore points preserved. Unfortunately this was never finished but could have been updated for 7 if it had.
[Download] Vista Hide 'n Seek BETA - The NeoSmart Forums