I just installed Hiren's on my USB Flash Drive, and every time I try to boot Vista without it, I get this error message:

Try (hd0,0): NTFS5: No grldr
Try (hd0,1): non-MS: skip
Try (hd0,2): NTFS5: No grldr
Try (hd0,3) invalid or null
Try (fd0): invalid or null

Cannot find GRLDR.

Press space bar to hold the screen, any other key to boot previous MBR.

Please help! I can't boot Vista without this Flash Drive!The PROBLEM you describe has happened before. A search through the CH archives shows that others have had difficulty using the program. You mentioned. That program is not from Microsoft, nor is it recommended by Microsoft, nor is it needed for normal operation of your computer.
With Vista f or any other Windows operating system having a backup plan is a requirement, not really an option. It is the user's responsibility to schedule and make backups on a regular basis. Windows does not do that for you, unless you ask it to.
Yes, I know it sounds like I'm being sarcastic, but I really am trying to be as nice as possible. What you have done is your own responsibility. Having said that, here are the steps you can take to recover your system.
You already should have a spare hard drive. If you don't, now is the time to acquire one. On a brand-new or clean used drives, do a complete installation of Windows with the appropriate drivers for your computer. Having done that, you'll be able to take the old drive and make it a slave on your computer. Then you'll be able to access it as the second drive and get  the important files you have on the original hard drive.
Although this is a time-consuming process, it is predictable and RELATIVELY easy and does not require great knowledge or understanding of how the system works. Basically, you just start over again and recover your documents from the old drive. Fairly simple.
Otherwise, trying to FIGURE out what has been damaged in  the operating system is a slow trial and error process. Unless you already GONE through this before. It is possible to recover using a repair disk, but it needs to be a repair disk that works according to the Microsoft rules. You create such a repair disk after you do a clean install of the operating system. All this has been documented here on this site and also in the Microsoft knowledge base.
Any time a person gets a new computer with the Microsoft operating system on it, creation of a repair or recovery disk should be considered  s  needed task. The restore PARTITION provided by the manufacturer does not let you preserve your data in the documents and settings file. The restore partition is only an emergency method to get the system back to the original factory settings. The user has to make his own scheme n for saving his documents and settings.
That is about all I have to say on that the subject. I for one, and some others here, do not recommend using the program that you put  on your computer.

http://en.wikipedia.org/wiki/Hiren%27s_BootCD
Hiren's BootCD

This was done from dictation. Excuse grimmer errors.