windows 7 - Removing old XP partition, but it's the active, system partition

Although my active partition contains the old XP installation, the secanario described in

Removing old Vista partition, but it's the active, system partition

exactly matches mine. I finally need the space and want to get rid of that old and long unsused partition.

The way via Windows 7 DVD boot and revovery seemed to work, so I decided to give it a try.

Initial situation: 1. partition is WinXP mapped to drive X: in windows 7 2. partition is Win7 mapped to drive C: in windows 7

Arconis Disk Directory says parition 1 (XP) is "Active, System, Bootable", partition 2 is "Bootable". I made partition 2 the active one and then rebooted using Win7 DVD. As Andy mentioned it nedeed several reboots when Windows Repair found in error after the other until it finally said everything is ok.

However, when trying to boot from the HD, I now get:

"A disk read error occurred" "Press Ctrl+Alt+Del to restart"

Does anyone have a clue what's missing?

Note that I (luckily) had not yet deleted the old XP partition, so I could change it back to be the active one and Windows 7 came back.

I'm scared to delete the XP partition since I do not understand what the problem is.