Mount XP in read/write mode:

mount -t ntfs-3g /dev/sda1 /mnt/windows

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centos - I always forget this:

Nothing beats the Slax 6.0 "live Linux CD" for mounting a file system and repairing a filesystem, copying files, etc. However, where an LVM volume is concerned there's a bit more tinkering involved and I will surely forget how this is done (half awake I added something to /etc/rc.d/rc.local the other night and my system would not boot). Normally, with Slax, you just go to /mnt and you'll see NTFS and ext3 style partitions. However, you need to do the following with something like Centos:

vgscan -v (find any LVM volumes)
vgchange -a y (activate them)

then...

mkdir -p /mnt/VolGroup00/LogVol00
mount /dev/VolGroup00/LogVol00 /mnt/VolGroup00/LogVol00