My matser hd oin is aet to master. My slave is set

The first thing you need to do is edit the boot.ini file

http://support.microsoft.com/kb/289022

This will explain how to do that.

This part is only an example and wont be what u got prob in your boot inifile......
line 1
multi(0)disk(0)rdisk(0)partition(1)WINDOWS="Windows XP Professional" /fastdetect

line 2

multi(0)disk(1)rdisk(0)partition(1)WINDOWS="Windows XP Professional" /fastdetect

(end of sample)

you need to make sure

multi(0)disk(0)rdisk(0)partition is listed first the one with all (o)
and then list the other, you may just have to copy and paste..
but the boot.ini file basicaly tells your computer what order to boot the disks in.

(you can also do this by going into bios setup when you start your comptuer, just read it when your comptuer boots up what button to press to get into it, normaly its like f8.)

but u can change the boot order under that also.
Once u have changed your boot order either by bios or using the boot.ini file way, u should be able to just format, drive 2 (slave)..

reinstalling windows on it wont even be necessary.

Two things, make sure nothing is left on the drive and be sure windows XP is not loading from that drive. Quick way to check that is to disconnect the ribbon cable so Windows won't see the drive at startup.

If ready, you can format the drive by open My Computer (or Windows Explorer and drill down to the drive level). Right click on the desired drive and select format. Follow instructs from there. You can select the quick format option. This will wipe all contents from that drive.

If you have the XP install disc just disconnect your master HD and use XP disc to format the slave drive. Exit after format, remove XP disc and reconnect Master. You now only have 1 drive with an OS.