I have the same problem.
On a new laptop with Windows 7, I disabled McAfee, ran ccs_setup_5.5.0.00077.exe and got message:
Invalid URL, Unable to access
http://software-dl.ti.com/dsps/dsps_public_sw/sdo_ccstudio/CCSv5/CCS5.5.0.00077_win32
Check your setting and try again.