Q: Can I upload epub files for sale to the store with a Windows computer or do I need a Mac?

Try it and find out.

Segue Foundation wrote:

 

Will the iStore accept files from a Windows computer?

No.  To publish directly to Apple's iBookstore requires apps like iTunes Producer that only run on a Mac.  You can publish indirectly by using an Aggregator. I also think there are organizations that let you rent access to a Mac online.  For more general info see the FAQ

http://www.apple.com/itunes/working-itunes/sell-content/books/book-faq.html