Lotus 8.5 Trial Version Will Not Install

I downloaded and am trying to install the “IBM Lotus Notes 8.5 for Windows XP and Visa English Trial C1SB9EN.EXE” I am getting this error message: “Cannot upgrade AllClient installation to Notes client.”

The Vista Business computer that I am working on has a full version 5.1 client install (Notes, Designer, Adminstrator). I cannot uninstall this software at this time.

Some background: 6 years ago I was a Principal Certified Developer on V5. I am trying to get back into the game by loading 8.5 to understand the operational and developer enviroment. If there is a better way to get up to speed, please let me know.