quite simply, after a partition has been created you are in no trouble, no more risk than a folder.
The problem is when you create/modify them, it's a risky business, I have lost count of the number of times I have repartitioned my drives and whatever program I have used (be it partition magic/commander, fdisk, whatever) has come accross an error of some sort, and totally fubared the parition table or my disk.
I've had this arguement before on here, and there were two 'camps' then, and I don't expect to change your mind, but in my personal experience partitioning is a bad idea, something that just isn't really needed anymore now that we have OS's that can cope with large hard drives. Want to re-install windows without losing all your data? Just overwrite it, windowsXP does a pretty good job of deleting the old install before installnig itself again.