"online" told me that for HP BIOS need a special modification in boot sector.
In your case the HP BIOS could be the "special" culprit.
In order to boot from HP machines the trick should be to "nope" your UFD BootSector with an HexEditor as following:
if the (1st) partition is formatted in FAT32 file-system from offset 0x7EE6 (Decimal=32486) to offset 0x7EE9 (Decimal=32489) set the existing values as 90 (4 bytes);
if it is formatted in NTFS file-system set as 90 the existing values from offset 0x7ED9 (Decimal=32473) to offset 0x7EDC (Decimal=32476) - 4 bytes.
Please, see here too
Hoping it helps.
I've tryed without success. Maybe was something wrong, I don't know, maybe I do something wrong.
I tried "RMPrepUSB".
Here a solution that works for me.
1. Download RMPrepUSB ==> http://www.boot-land...?showtopic=7739
2. Start "RMBPREPUSB.EXE"
3. Choose option, NTFS + "Boot as HDD (2PTNS)" + "XP bootable (NTFS)
4. click "Prepare Drive"
6. You got a message in a command.com windows if progress was successful.
7. Afterwards I copy folowing files from a installed Windows XP System on USB-Stick:
8. The "boot.ini" I have modified, copy this text in "boot.ini"
[boot loader] timeout=30 default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS [operating systems] multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="FAKE ENTRY - NO EFFECT" C:\grldr="START GRUB4DOS"9. Copy latest "grldr" and your modified "menue.lst" on your USB-Stick.
9. I use "grubinst_gui.exe" and create "grub mbr".
10. Finish, this works for me and USB-Stick boot on HP Computers.