Hey guys, i find a solution to change the partition type without formating: use sfdisk (under linux).

#/ sfdisk -d /dev/hdx > dump
--> this will give you the partition table in "human readable" format. Edit the file "dump" and change the appropriate partition type numbers (linux=83, ntfs=7, ...). Save the file and:
#/ sfdisk -f /dev/hdx < dump
--> this will replace the partition table with the one you defined in "dump". That's all!

I also recommend GRUB: it's the better bootloader ever!

You should follow this advice:
[Originally posted by Drogo]
"1-Create a Rescue disk set from partition magic
2-boot up from those disks and enable the windows partiton

PS: if you didn´t create the rescue disks, then you must install partion magic on a diff comp. to create those disks..."

I had the same problem as you ("autochk not found") after I tried to boot RedHat, Mandrake and Windows from Grub (or Lilo). My computer got all mixed up. I was unable to start Windows. I tried every possible fix before I saw Drogo´s post. Everything was fixed by following his advice. Partion Magic is a wonderful program!!! Saved me from formatting. Thanks Drogo!

Thank you for your advice.
But I think Linux users will prefer the 'sfdisk' solution described above

I never had the same problem again so if it was a bug in GRUB I suppose it has been fixed.