When running this in SQL2005 I get the following response (after answering the question)

Msg 139, Level 15, State 1, Line 0

Cannot assign a default value to a local variable.

Msg 137, Level 15, State 2, Line 7

Must declare the scalar variable "@CustAccount".

You can not set the value of a variable at the same time as declaring it until SQL 2008.