You should be able to boot to your XP fine..you just need to configure your /boot/grub/menu.lst so it contains an entry for XP. Ubuntu forums or these LQ forums have lots of info about how a dual boot is configured (it's really a matter of 2-3 lines).
And about the "accessing". Because it's an NTFS drive, you can access it read-only fine, but if you want to write data there, you might have problems. You can add to your /etc/fstab a line like this:
/dev/hdb1 /mnt/windows ntfs defaults 0 0
that would mount /dev/hdb1 (change that to the device which your 2nd HD really is, if it's not that) to /mnt/windows (remember to create that directory, or point it someplace else) with ntfs-filesystem and default options. Read
to see more information about what options you can give (like "auto,umask=0222" to automatically mount it at boot and let other users use it too, not just the one who mounts it [root]).
if you need a write access you'll need either ntfs-fuse drivers installed (and ntfs-tools package) or then use Captive (only for 32-bit systems); you can read more about them by googling Captive and/or ntfs-fuse. Neither of them gives you "full good" write access; ntfs-fuse has a 50/50 chance to success writing data and a bit bigger for deleting it. So a lot of it is going to fail. Captive is said to have some big problems at the moment, so none of them will give you a smooth working write-access; I'd say forget it for the moment. Use a fat32 filesystem, rather, for windows if you can..