Two HDDs on one board

I am trying to have two drives on one mobo. Both have Windows XP but only one is bootable in BIOS. I am able to launch Windows and see both drives. When I click on the drive that houses my data files I see it as drive D but access is denied. I can launch some programmes on the same drive in the Programe File folder but the D: drive access is denied, where I presume the data files are.

There is another folder called Shared Folder but there is nothing there. When this D: drive was my main drive my files were in My Documents. I can't see that now; just the D: drive folder, with access denied.

My main bootable drive has Windows XP SP3 and the drive I am trying to access my data files on has Windows XP Home SP2. My system is a Gigabyte GA-880GA-UD3H board, AMD Phenom IIx2 555 BE and RAM is two sticks of 2GB DDR3 RAM. The main bootable drive is a WD 500 GB Sata3 drive. The old drive I am trying to access is a Maxtor 160GB which is now 4 years old but works fine on my old board which was a MSI MS-6702 running an Athlon single core CPU.