problems with sysinstall

The first one: when I install -current on disk where WinXP on first 
slice, sysinstall brakes WinXP boot complete. I got 'Missing operation 
system' everytime. Even I've tried 'fixboot' and reinstall WinXP.
Helps only 'dd if=/dev/zero of=/dev/ad0 count=100' and reinstall WinXP 
on clean disk.

When I've installed first -current on first slice and second -current on 
second slice I got booting only first one. I use grub and either I set 
root(hd1,0) or root(hd1,1) (yes, it's a second disk) and 'chainloader 
+1' and 'boot' I've got always first -current boot. Looks like problem 
with boot sector where hardcoded booting from first slice (?).

The second: when I've tried to save results from Fdisk or Label menu 
I've got the message: 'ERROR: Unable to write data to disk ad0!'
Why? I can change slices and partitions only when I boot from CD-ROM.

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Sem.