1) Open the main pack 2008_05_06_01_webvulnscan5.rar
2) Install Acunetix with 2008_05_06_01_webvulnscan5.exe (this is latest build)
3) Crack wvs.exe with the provided crack wvs_crck.exe
4) (optional) Apply 2 acunetix patches by unpacking wvs5-build2738-update-last.exe to your Acunetix installation directory (they are update patch_38-39 and patch_39-40 if you want to know exactly)
Most functions are working fine, the auto update does not work.
You now have Acunetix 5.1 latest build Enterprise Edition