If I let XP boot, (it is the default) it comes up fine. If I choose to start Vista I get a blue screen that only shows for a second or two. It basically says that the boot sector is bad and I should do a repair of Vista with my original CD. To get my system back, I reload Vista from a Ghost that I did just before the upgrade to SP1. I've tried to upgrade Vista to SP1 twice, with the same result.
I have EasyBCD loaded on the Vista partition, with XP as the default OS. In the "View Settings tab are the following items:
Name: Microsoft Windows XP
BCD ID: (ntldr)
Bootloader Path: \ntldr
I downloaded the software and instructions. I'm travelling right now and don't have high speed Internet access right now, so I may not be able to test this with the SP1 upgrade for a week of so. I'll get back with a post once I can.
EasyBCD is just an editing tool. You don't need to remove it. In fact when you've got HnS successfully booting and hiding things for you, you'll use EasyBCD to edit the timeout to 0 in Vista's menu to remove the second (now redundant) boot menu. (Unless you have 2 Vistas, in which case the second menu will allow you to chose between them).
HnS surplants the Vista bootloader, and hands control to XP itself (after doing the hiding), so the Vista BCD no longer has to do that task - hence set its timeout to zero once you're happy that HnS is doing what you want)
Don't change or delete anything else in the BCD though. It's handy to have it all there as a fallback if Vista overwrites the bootmanager and resumes control (as it did with SP1)