You can install SSIS from sql server 2005 or above,
the first link Ramjaddu proposed is for sql server 2008 R2 evaluation version
and second link which SSISJoost proposed is for sql server 2011 denali CTP3.
the sql server 2008 R2 is latest stable version of sql server, but it will be replaced with SSIS 2011 soon.
My Submitted sessions at sqlbits.com