Hi, I have a sata 2, 320gb hdd and an ide 400gb. My ide is set to primary slave, access mode=auto. I am using Windows Vista and XP together, as dual boot. I am booting both the operating systems through my 320gb sata2. The 400gb ide is working without any pblems in windows vista, but in xp in - COMPUTER managemnt > Disk Management i am GETTING my 400gb ide as online (healty, Gpt Protective Partition) and i cannot click on any more options.So you can access the hard drive in Vista, but not in XP?

Any errors in Device Manager? (yellow question marks or exclamation marks)If you right click it and select Properties what is being reported ? ?
Do this on both machines...XP can't read GPT partitions...that's why.

If you want XP to access that data, you'll have to copy it all to another drive. Reformat the offending drive (preferrably in XP so you don't accidentally create GPT partitions again in Vista), then copy your data back.thanks a lot guys, no errors nothing in device manager(though i cant click on any option except help) and i can access it in vista without any problems. Is there any other way around killer killerb255 to read it in xp, coz BACKING up 400gb of data is going to be a *censored* of a TASK .Take a gander at these articles:

http://www.microsoft.com/whdc/device/storage/GPT_FAQ.mspx
http://technet.microsoft.com/en-us/library/cc737510.aspx

According to the second article, the only way to change from GPT back to MBR (old skool partitions) is to format...

There may be THIRD party tools out there to get around that problem (similar to going from NTFS to FAT/FAT32 or from Dynamic to Basic disks--normally you have to format), but you'll be taking a BIG risk with your data using those...