Both answers provided are correct.
1. Adobe doesn't officially support Acrobat 8 Std/Pro on Windows 7. This may change depending on Adobe.
2. After installing Acrobat 8 Std or Pro you will want to update it. Bringing it to the latest update/release corrects most reported issues with running Acrobat 8 on Windows 7. If you do not upgrade/patch after installing, a number of issues will be present, one being that you can't load Acrobat or it crashing shortly after opening it.
I myself have tested it on Windows 7 Professional (x86), Enterprise (x86), and Ultimate (x64) it is running fine.