Seen a few people making topics about hitting the issue with WinXP64 and XIV reporting that their is insufficient space left on the drive (space remaining is reported as %dGB instead of an actual file size). I have tried a few things to work out what is causing the bug and write something to fix it a bit more gracefully than what I am about to suggest, but so far have not found the cause. The variable %d is not being correctly calculated and thus when the installer performs its maths check to make sure drive space free is greater than what is required, it fails. I thought it was an issue with .NET but doesn't seem to be.
First of all, download and install Application Verifier from Microsoft. You can get it from here:
Now, follow these instructions:
1) Load the x86 version of Application Verifier (simply called Application Verifier, not the x64 version which is labeled thusly).
2) Go to File > New Application and find your ffxivsetup.exe
3) Click ffxisetup.exe under the Applications list on the left, and in the right expand Compatability and tick "HighVersionLie".
4) Right click HighVersionLie and select Properties, give it the following properties:
Major version: 5
Minor version: 1
Build number: 2600
Service pack major: 3
Service pack minor: 0
Suite mask: 0
Product type: 0
CSD version: (leave blank)
5) Hit OK to the properties, save, and exit.
6) Double click your ffxisetup.exe icon
If anyone can shed some light on the true underlying cause that would be great. Manually editing your registry with the above settings doesn't seem to be enough. Anyway, performing the above steps is a workaround for now.
Interestingly, this issue did not occur at all during any of the Alpha tests, and was only introduced in the Beta. SE have been notified of the issue, but have made no acknowledgments towards it so it might not be fixed even in the retail version. Then again, the required spec was changed to specify SP3 for XP so that is their get out clause :)