drive partition not accessible - access is denied

I've just put together my new PC, with Vista Home Premium 64bit OEM on a brand new drive.

After installing I plugged in my old drive as well, this has two partitions, the first has XP Pro installed, the second all my music/videos/photos/general data store. Under XP this partition was shared over my flat network, with a password so only I could access it from my laptop (simple file sharing had to be turned off to set this up if I remember correctly).

Now under Vista I can't seem to access this partition using explorer. The partition can be accessed by things like the Vista backup utility and I have perfect access to the first partition on the disk.

There must be some simple way to access the stuff on this partition going through the process of using Vista backup to back up the data onto the new drive and repartition/format the old drive, then restoring the data back onto the old drive.

Could it be that there is something wrong with the partition table, or is it caused by the shared access I had set up? The partition worked fine under XP.

New system config is:
Gigabyte GA-MA790X-DS4 MB
Phenom 9550
4GB DDRII 800 Adata (4GB more in the post from the supplier, it's so cheap!)
Gigabyte NX96T512HP 9600GT
Seagate 320GB SATA (Old HDD)
Seagate 500GB SATA (New HDD)
packed away in a Lian Li PC7 II Case.