Hey Ricard0, for starters it seems that you have no valid entry for "Earlier Version of Windows" in your Vista bootloader, although why this should prevent Vista from booting is a mystery to me -- it's possible that Vista did not copy the file into your Vista partition, because it already exists in your XP, but then when attempting to load cannot find it in the XP because the OS is not accounted for in the boot loader, so needs the DVD.
I think there are basically four ways to solve your problem --- one long and easy, one more fiddly, and not guaranteed to work (given also the fact that the Vista pre-boot environment can do strange things with drive order), third long and similar to but a little more fiddly than 1) if the first two don't work, fourth long and a bit fiddly, if this is for Vista x64 ...
1) Easy and long would be to boot into XP, format your Vista partition, then from within XP pop the DVD in and run setup from within Windows XP. This would mean trashing your current Vista setup, but is almost guaranteed to ensure the creation of a proper dual-boot environment. You will not be able to run Vista x64 Setup from normal Windows XP using this method BTW
2) Fiddly and definitely not guaranteed to work would be to attempt adding the "Legacy" boot option to your Vista boot loader from within Vista ; this is especially
not guaranteed to remove the necessity to boot from DVD, so I personally would not recommend this option, as you could easily end up with just losing the ability to boot into Vista at all, and needing to start from scratch anyway...
3) Third possibility is to boot to XP and format your Vista partition as above, but then create a small (new) partition, copy the entire contents of the DVD into that partition, then in XP, run Setup from there, bearing in mind you will still not be able to run Vista x64 Setup from normal Windows XP. All in all, this would be the safest option IMO
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You could also await the forthcoming new version of VistaBootPRO, but in your shoes I'd just reinstall
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(Fourth solution if this is a Vista x64 / XP 32-bit dual-boot)
4) Do a "repair" install of XP, without formatting the partition (easiest way to do this is boot into XP, pop the XP CD into the tray, choose Upgrade option ; this will remove the Vista boot option, but NOT the BCD boot data files ; go into XP Safe Mode and delete the "Documents and Settings", "Program Files", "Program Files (x86)", "Users", and "Windows" folders in your Vista partition ; reboot and reinstall a clean copy of Vista x64, booting from the Vista DVD, and without formatting.
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Whatever you do, don't fiddle around with the boot order settings in BIOS when dual booting Vista Beta 2 and XP ...