adding arch boot to ubuntu laptop--a couple questions
 

I'm currently running a windows/ubuntu dual boot on my laptop, and I'm planning on making it a triple-boot by adding arch linux. At this point I have 2 questions:

1) Where should I add the partitions to my current partition table for the new arch installation? Will I loose data by adding partitions, or will it just use the free space without deleting any current data? I'll be adding 3 new partitions, one each for root, boot and swap. For data I want to share my current data partition from the ubuntu installation and be able to access it from both OS's.

2) My second question is about sharing the data partition. My ubuntu data partition is encrypted, so I'm wondering whether it will be possible to access the data on it from the new arch installation. If so, how do I do this?

1) You do not need another boot and swap.

To free/unallocated space.

You should not lose any data if you do it right. That is, if you create the partitions from free/unallocated space. As pointed out above, if yuo already have a swap partition, it is pointless to create another. Why a separate boot partition? Do you have one now for Ubuntu?

If you have a separate data partition, you would need to create a mount point in Arch then an appropriate entry in the /etc/fstab file so it is available on boot. You can find how to do this just doing an online search as there are thousands of sites explaining it with specific examples. I don't use encryption so don't know how you would access it.

Thanks for your answers. That answers all my questions except the one about accessing the encrypted data drive from arch. I used the drive encryption option while installing ubuntu from the .iso, so I'm wondering if there's a way to configure the arch installation to allow me to decrypt the data drive during boot, using the same password.

Do you have free space, or is it all allocated to the windows, linux and swap partitions?

I've made a triple boot system from a dual boot system. It seemed to work best if I backed up any data in the original linux partition and deleted the linux and swap partitions. The free space was made an extended partition with 4 logical partitions -- swap, ext4 for linux OS 1, ext4 for linux OS 2, ext4 for data. None of the partitions was encrypted during installation. The data partition could be accessed from both linux OS partitions. There may be better ways to set the disk up, but I feel safer setting up the partitions the way I want rather than leaving it to the installer.

Tip: Use same UID for user in your new install to retain files ownership.