I don’t know if someone have done it before but i could install Xcode 3 on Lion.
It also supports ASS
This are the images:
http://www.foto-me.ru/v.php?id=e7105cef3f07d983c920df9462f86cd7
http://www.save-img.com/v.php?id=6d4d249693f8d4a2235f9a8a4368bdc6
Yes, you can install Xcode 3 on Lion. I am living proof that it works.
BUT (there’s always a but 
) if you do you will not be able to validate and upload apps to the mac app store using Xcode 4, even if you install it after. This is something I have discovered after hours of excahnge with developer support.
There is reasons why you can’t have Xcode 3 on Lion, and this is one of them.
Just something I thought anyone reading this should be aware of.
Model: MacBookPro8,2
Browser: Safari 534.51.22
Operating System: Mac OS X (10.7)