Is there any trick that allows to use Management Studio's (ver. 2008) IntelliSense feature with earlier versions of SQL Server?
There's no known trick 'in the wild' for getting around this, other than using CTP-6 of SQL Server 2008 (in favour of the RTM).
the reasons for removing backward compatability (and a lot more discussion besides) are provided at the relevant feedback in microsoft connect.
edit: sorry i don't know where this ctp is available, if at all
Has anyone tried either patching SSMS not to check the version (perhaps try looking at the binary differences between CTP 6 and RTM?), or patching SS 2005 to pretend to be 2008?
Unclean, I know, but I don't see any other way.