For starters this is still a new science and many people have had good luck with at least one of these methods and others have not. Note that flash drives are often also called thumb drives, keychain drives, pendrives, etc.
A FEW THINGS YOU NEED TO CONSIDER IN ADVANCE.
1. The PC has to support booting from a USB flash drive. There may be anywhere from 1-3 items to change in the BIOS to make this possible assuming your BIOS supports it. Some bios's may refer to your flash drive as a USB floppy or USB zip.
2. The USB flash drive must support booting from it in general.
3. The flash drive must contain the boot/system files.
4. The flash drive must have bootsector area. This is done with special utilities.
5. References to "A:" drive lines in the autoexec.bat and/or config.sys files you copy to the drive after you make it bootable may result in errors.
6. You "may" have to format your floppy disk first in WinXP before you create a bootdisk as XP may "not" like working later on with a disk formatted otherwise.
7. Included below is a bootable ISO of DOS 7.1 which may be used with some of these methods if you do not have a 1.44 drive.
METHODS
Method 1 - Make your flash drive bootable using Bart's mkbt util:
http://www.nu2.nu/mkbt/ | Alt: mkbt20.zip
Put a bootable floppy disk in your A: drive or create one using Windows.
Download mkbt20.zip and unpack to to new temp folder you create.
Go to the temp folder.
Extract the bootsector from the bootable floppy disk. eg Open a DOS Window and go to the directory where you extracted MKBT. Type:
mkbt -c a: bootsect.bin
The boot sectors from the bootable floppy disk have just been saved to a file in the temp folder you created.
Format the flash drive in FAT or FAT16.
Copy the bootsector to the flash drive. Open a DOS Window and go to the folder where you extracted MKBT. Type:
mkbt -x bootsect.bin Z:
"Z" represents the flash drive drive Letter. So if your flash drive has another drive letter, then change the "Z" accordingly.
Now you can [grin] "should" be able to copy the utils you need to the pen drive.
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Method 2 - Try these 2 HP/Compaq USB Flash Drive Utilities. They work with many other brands of flash drives as well.
HP USB Disk Storage Format Tool Version 2.0.6
HP Drive Key Boot Utility Version 7.41
Download
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Method 3 - Third Party Links
http://ucsu.colorado.edu/~shaher/Bootable_USB.html
Recall I did say it's a new science.
http://www.microsoft.com/whdc/device/storage/usb-boot.mspx
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Method 4 - A Bootdisk.Com Visitor Suggested
Here is my another method for creating dos bootable USB sticks using windows format.
1. From Win98 DOS-Prompt type "SYS {USBDriveLetter}:" or "FORMAT {USBDriveLetter} /U /S". If from WinXp then from start->run command.com execute format.exe copied from win95 or win98.
OR
2. Simply by enabling copy system files in windows explorer format window. By default it is disabled for non-floppy drives. To enable it use windows enabler program from http://www.angelfire.com/falcon/speedload/Enabler.htm an whoila it works
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Method 5 - Another Bootdisk.Com Fan Suggested - Thanks Keith
First if you don't have a physical floppy drive (and don't want one) you can use the [free] "virtual floppy driver" from here:
http://chitchat.at.infoseek.co.jp/vmware/vfd.html
With that you get an A: drive and can manipulate a floppy image as if you were using real floppy. You can then use that image to make a bootable CD. It's not that user friendly but once you get how it works it does work perfectly.
Even cooler you can use a "raw write" utility like dd for windows to write the floppy image directly to your USB thumb drive. Even without that famous HP utility to do the magic this will make your USB thumb drive bootable. The 'dd' ported to Windows is located here:
Another trick you can use with that dd utility involves MS VritualPC (which is free). You can create a virtual machine/virtual hard drive, set it up the way you want then use dd to "raw write" the virtual hard drive image to the thumb drive; this will make the thumb drive identical to the image, including bootable (again, no HP utilities required).
Of course, your thumb drive will effectively have the capacity the size if the image in question (your 1GB flash drive will effectively be 1.44 Megs).
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