I'm installing Ubuntu (or Xubuntu/Lubuntu/Kubuntu) alongside Windows 7/XP. I got to the screen that says, "Allocate drive space by dragging the slider below." On the following screen, I'm not sure whether the right side or the left side is for Ubuntu or for Windows. Which side is which?
It is on the right hand side. Yes, Ubuntu is on the right hand side of the slider. See the below picture.
I wanted to see this by doing a needless actual install, And also wanted to take a screenshot, with Alt key pressing, To my surprise, As soon as I press ALT, It revealed the actual partition of Ubuntu !!
If Windows was installed previously, it will typically be located in the beginning of the partition; meaning it will be the first, left-most part of the bar.
Caution: this might not be your case. A screenshot or diagram of some kind would be helpful.
//After selecting "install along side windows 7" and you enter the easy partitioning press alt to view which side is which. Windows is usally on the left, but after pressing alt it will tell you which side is Ubuntu.
I agree that this dialog is confusing and should be improved.
Meanwhile, one workaround is:
use some tool to get more information about the current partitions -- for example, boot from a liveUSB and use gparted or cfdisk. As Nirmik pointed out, the Windows partition will be NTFS (or possibly FAT or FAT32) and probably the first partition.
write down the exact size of all the partitions on a piece of paper, and note which one is the Windows partition.
Later, when you get to that setup screen, look at the size shown on the screen for each partition, and try match them up with the sizes you have written on paper.