Did not successfully update the MBR

Greetings.
I'm finding I can't get set up with a bootable media!

I've tried a small USB HDD and OCZ 8GB Flash Drive.
Format both to Fat32 and mount as E:
Copy unzipped directories to E:
CD to boot and run bootinst.exe

Here's what I get:

Code:

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E:\boot>bootinst.exe e:

 WARNING!
 Master Boot Record (MBR) of the drive E: will be overwritten.

 Press any key to continue, or ctrl-c to abortAccessing physical drive: Access i
s denied.
Did not successfully update the MBR; continuing...


 Disk E: is bootable now.
 Installation succesfull.

Press any key to continue...

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I'm running Windows 7 on my desktop, but I've also tried same with XP...

How do I fix this?