Windows 7 is the minimum version of Windows supported as this is a reasonable base level to support despite it & other versions of Windows having gone end of life versus development resources available (aka just myself).
A processor (CPU) which has SSE2 support will be required as even though most of the code created for WACUP will not be able to benefit from this processor feature, for certain aspects it will and that is why it's considered a requirement.
A working internet connection is required to allow the WACUP installer to download the Winamp 5.666 patched installer on your behalf or you can pre-download a copy of the Winamp 5.666 patched installer & place that in the same folder as the WACUP installer. Please note that some aspects which are selected in the installer may not be installed if there is no working internet connection though it shouldn't prevent the WACUP installer from continuing as long as the Winamp 5.666 patched installer is available to allow the WACUP installer to get the core files needed.
Note: When WACUP no longer has any core requirements for the Winamp 5.666 exe / plug-ins then an offline version of the WACUP installer will eventually be made available as it's not really viable for them to be included in the WACUP installer due to the fun of licensing even if it's related to an abandoned release of software.
If you're having issues with downloading & running the WACUP installer due to it being blocked by your anti-virus / malware protection software then please see here for more information about commonly seen false positive detections & how you can resolve the issue if you're happy that it is a false positive (e.g. allowing it to be run & to gain the trust needed to allow it through such checks).
Alternatively there's numerous ways to contact me & let me know about the issue or have a chat to answer any questions you might have about the safety of using WACUP.