Don't use fdisk /mbr... you just need to edit boot.ini as ilh said. You can get to it through the system applet in control panel as he explained, but it might be a bit quicker just to open it directly in Notepad. It's a hidden system file in the root of the C drive, so you need to unset the attributes by bringing up a DOS prompt, entering "cd c:\" and then "attrib -h -s boot.ini." Then you can just type "notepad boot.ini" to open it in Notepad, where you should see something like this:
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(1)partition(1)\WINDOWS="Microsoft Windows XP Professional" /fastdetect
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Professional" /fastdetect
The Windows installation you want to get rid of on the second array should have the higher RDISK number, so that's the line you want to delete. Make sure the "default=" line is referring to the correct OS, so it looks like this:
[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="Microsoft Windows XP Professional" /fastdetect
With some controllers it might say "scsi" instead of "multi" but the same procedure applies.
Then save boot.ini, reset the hidden and system attributes by entering "attrib +h +s boot.ini", cross your fingers, reboot and the system should boot straight into your desired OS without bringing up a boot menu. Then you can just delete the Windows installation on the second array...probably best to reformat the partition to make sure it's completely gone (a quick format is good enough).
Hope this is the last of your headaches...
