Problems with ext harddisk

Hello,
am just wondering if any-1 can give any clues ...... i have an 80Gb ext harddrive installed on vista and working perfectly(except vista has no sound now!!??) now to the problem ....... i have xp installed on the same computer within the main drive but partitioned accordingly everything works fine except i have no way of accessing my ext harddisk i have tried many of the suggestions within this and various other forums but to no avail i feel that i may have to reformat the drive in vista to use on xp but risk losing ALOT of data in doing so any help in solving this problem would be much appreciated