Drive letters keep changing

Hi,

I have just replaced XP with Windows 7. I unplugged the old system disk and put in a new one in the same place, and then removed all its partitions with the Win7 installer and set up from scratch. The system disk is always a primary master on the motherboard ATA controller.

I have two USB hard drives permanently attached - a 320GB WD MyBook and a 500GB drive in an Integra case. I also have a 1.5TB internal RAID1 array using motherboard NVIDIA raid (SATA). Finally, a DVDRW occupies a third SATA port.

Under XP, I used disk management to assign letters as follows:
C: - ATA system drive
D: - 500GB external
E: - 320GB external
F: - DVDRW
G: - 1.5TB internal array

Upon installation of Win7, which went rather well, I used disk management to assign these drive letters. However, most of the time when I reboot, they change such that internal drives are assigned lower letters. This breaks my shortcuts and path references. I have re-assigned the drive letters in the intended configuration a few times now, but Win7 is adamant that these assignments only last until the next reboot. Win7's up to date now, but the problem is still there.

How can I make these drive letter assignments permanent, so that they persist through reboots?

Wonderful. Second method didn't work straight away - but after a restart they moved around, and ten reboots later they're stuck like anything. Thanks!