Microsoft boot managers do not have the ability to hide systems dynamically.
EasyBCD gives you a method by chaining the grub boot manager (which does hide/unhide).
However, this was an extremely clunky method, involving multiple boot menus, so it was replaced by HnS
How-To: Hide Vista Partition from XP with NeoGrub! | The NeoSmart Files
HnS does work in W7 (and W8).
It never made it out of Beta status, so it still refers to "Vista", but since Vista/7/8 all use the same bootmgr, the logic is unchanged and you can use it on W7 (just call it Vista).
You will not be able to hide XP from W7, only W7 from XP, because that's all that HnS is designed to do.
You don't necessarily need a dynamic hide facility anyway.
For most people, the following registry hack (applied in each XP) will prevent XP from damaging the W7 restore points and backups.
System Restore Points - Stop XP Dual Boot Delete - Vista Forums
Use HnS only if that doesn't work.
As I said, HnS is designed purely for that one purpose and what it does, in essence, is provide a GUI which helps you create a grub "menu.lst" which will hide Vista/7/8 from XP, then switches boot managers (by renaming) between bootmgr and grub.
Once that is done, you are of course perfectly at liberty to customize the grub menu to do anything of which it is capable (like mutual hiding).
The following thread might give you a better idea
Quad boot Vista, XP, W7 and Ubuntu using HnS to protect system restore points from XP