XP / Vista dual boot

I previously had a Vista Beta version, and XP configured on a system with separate partitions on the same physical IDE drive, in a dual-boot configuration. This worked fine, but when I re-installed the Vista partition with the full release version, I discovered that I am now unable to run ChkDsk from the XP partition.
I am able to verify that both partitions are in fine working order, if I check them from Vista, but if I schedule ChkDsk from the XP partition to run on the next restart, I get an error the the drive is locked and cannot open volume for access.
I am wondering if something running in the background on the Vista partition is locking the drive? If so, what might it be, and is there a way to disable that feature, or a work around that will enable disk checking on the other partition?