64-bit Winamp required.
Okay so before this page turns into a flame war, in truth, this has nothing to do with 64-bit architecture. I just redownloaded winamp to install it on a fresh install of windows 7 64-bit and got an error message telling me it was incompatible and may have been designed for 32 bit windows only. After I spent half an hour on google trying to find where the HELL the 64 bit download link for winamp was and reading through some INTENSE 2007-9 arguments about whether such a thing was even necessary I suddenly realised the error message was kind of generic, and perhaps it was just a corrupt download. This was in fact the case. So I'm putting this post here for anyone else who has the same problem in future.
And thus, if you download winamp and get a message telling you that the program is incompatible and may have been designed for a different architecture (32-bit or 64-bit), just delete the file, clear your cache, and download winamp again.