Branded HP systems do not accept Linux???

This last week, there was a second experience with branded HP systems. earlier at one of the colleagues requested me to provide partitions in his HP Pavillion that had unpartitioned 80 GB HDD. I used some Linux CD (I think Yoper) to run QT Parted, and did the thing. But then Windows XP failed to boot. I installed Xandros in one partition that identified XP and offerred dual boot. Even then, the Windows did not boot, there was not even an error message. I tried to recover Windows boot through rescue mode of Mandrake, no success. And I had to return home. The next day I provided my laptop Recovery CD that offers Repair option to this man. (He had 8 Recovery CDs that offered repartitioning and reinstalling to recover the system). My colleague reported that he even re-installed Windows from my CD, still the boot continued to fail. I suspected that he bungled somewhere. Anyway, not depending on me, he called HP people who again used the 8 recovery CDs and the status quo is brought back, the lone 80 GB partition. And the HP man said that with XP, no other operating system can be installed!!!!
Then this week, in my office, the CISCO boy (CISCO is our netwroking agency) asked me the same thing. And I did the same on this HP infinity system, and later even after attempting to recover from Repair option of another Windows CD or installing Xandros twice, Windows boot has not come back. FixMBR did not work. What may have gone wrong is a different matter but why these branded systems prefer not to create partitions?? On my Fujitsu Siemens (Amio 2020) too had a single 40 GB partition.
However,. in another HP infinity, it had a Recover partition created by Unistall. Uninstalling that and removing that partitions through Windows Admin. tools (Disk management), I could do what I wanted (in fact this is the system that now has Xandros PLUS Ubuntu over that, a triple boot option!! But the same HP infinity is not accepting sany other OS!!