Partitions, MBR & my headache!

[grumpyste]

I have created a Universal Windows XP image. The image contains only a capture of the C:\ (primary) partition.
We have a scripted image deployment method which is used when we PXE boot:-
1. Deletes all existing partitions from the PC
2. Creates a primary (C:\) and secondary (D:\) partition both NTFS, and sets the primary partition as active. Primary partition is set to take 60% of available space and secondary partition is set to take the remaining 40% of space.
3. Windows XP image is deployed to the primary partition
4. PC specific driver package is deployed
5. System reboots, Windows starts - sysprep kicks-in

Everything works fine in most cases, however we are having problems with some PC's which means that we have to use a DOS boot disk containing an app to erase the MBR and reformat the drive. Only after this process is done can we then complete steps 1-4 above.

From the prompt I have tried to clear/ delete the MBR using the following commands:

dd if=/dev/zero of=/dev/sda bs=512 count=1
or
dd if=/dev/zero of=/dev/sda bs=446 count=1

The commands complete successfully however after completing steps1-4 above the PC fails to boot.

Can someone help please?
How can I clean the MBR and format the hard drive within the linux environment prior to the scripted image process occuring?

Many thanks in advance,

Steve