So we stick with te original problem to install XP via USB. The DELL oem version gave the same error.
Today i installed XP on my mentioned dell gx260 via usb. I used a dane elec 4GB flash drive.
I finally overcome the 0x0000007B BSOD with help of the kicker.iso which is used in UBUSB. With this application I was able to come in a win environment and activate winnt32.exe.
1. First create your bartpe files using UBCD4WIN
2. after you have done that create your usb flashdrive using UBUSB
point to the files of your bartpe
be sure you check create cd image and let de default Z in place
check if you have selected the right drive
after finished you have a bootable usb drive which is able to get in a xp environment.
3. Now copy the content of your win XP CD to a folder XPCD on the flash drive (x:\xpcd)
4. after copying boot the drive in the PC and select Compatibility Mode (Memory Mapped)
5. after finished you select the commandline and type
X:\XPCD\i386\Winnt32.exe /syspart:C: /tempdrive:C: /makelocalsource
6. first enter the xpkey and name of the computer and region then click next
7. Now you're asked if you want to upgrade to the XP NTFS filesysten, select "NO" for this then hit Next.
8. It'll now see "Copying installation files" and the familiar green progress bar. Shortly after "Copying Installation Files" is complete, setup will close without notice or any type of prompt, this is normal.
9. remove the flash drive and Reboot your computer and setup will continue from the hard drive where you can choose to install XP or do a repair install if XP is already installed.
Many thanks to pcuser