I guess the question before you proceed is this:
Do you still want to keep the Vista Beta as a boot option? If not, there's an easy way to overwrite it's boot manager.
If you do, you are going to have to repair the boot manager/loader for Vista.
I'm going to assume you want to keep Vista for now. So let's proceed with that theory.
Follow the instructions on this Microsoft Support Page. It involves booting from the Vista DVD. Here's the part to follow first from the support page
http://support.microsoft.com/kb/927392/en-us:
How to repair the bootmanager from the command line:
(I'm starting the copy/paste from the pertinent part of the support page. You've already tried the first part of the support page's instructions)
----------------------------------------------Info starts here---------------------------------------
MORE INFORMATION
To run the Bootrec.exe tool, you must start Windows RE. To do this, follow these steps:
1. Put the Windows Vista installation disc in the disc drive, and then start the computer.
2. Press a key when you are prompted.
3. Select a language, a time, a currency, a keyboard or an input method, and then click Next.
4. Click Repair your computer.
5. Click the operating system that you want to repair, and then click Next.
6. In the System Recovery Options dialog box, click Command Prompt.
7. Type Bootrec.exe, and then press ENTER.
Bootrec.exe options
The Bootrec.exe tool supports the following options. Use the option that is appropriate for your situation.
Note If rebuilding the BCD does not resolve the startup issue, you can export and delete the BCD, and then run this option again. By doing this, you make sure that the BCD is completely rebuilt. To do this, type the following commands at the Windows RE command prompt:
? bcdedit /export C:\BCD_Backup
? c:
? cd boot
? attrib bcd -s -h -r
? ren c:\boot\bcd bcd.old
? bootrec /RebuildBcd
-----------------------------------end of instructions for now----------------------------------
Try rebooting after running that command sequence. Remember, you're doing this from the Recovery Environment command line part of the Vista DVD, not BartPE.
If still no go, try some of the other bootrec.exe switches mentioned later in the article.