seperate data partition used both xp vista

Hi,
I am using Beta2 of Vista via MSDN.
I currently have 3 partitions on my hard drive, 1 for XP Pro, 1 for Vista and 1 for data. The data drive (E:) I want to be able to access and use from both XP and Vista.
In XP all I do is point 'my documents' at the root of my data drive and all is good, however in Vista I cannot seem to do this and I can get read access to my data drive which is not very useful. I could do a blanket permission change on my data drive but I would like to understand if there is a better way.
Thanks in advance.
Vortal