I use WinMe and I upolad files via FTP all the time with no problems, except one. Because of the way my webhost has set up Apache, I cannot write or append to these files. Apache owns them, not me.
However, if I allow my PHP script to create the file on their server, I can then append or write to it. But I can't edit the file. IOW, if I download the file, edit it locally, and upload it, it then takes away my write priviliges -- not very useful.
Changing directory permissions doesn't help much either. Any file I upload via FTP is still owned by the server, not me.
And yes, I am looking for a new webhost who can get this thing right.
I don't know if that sheds any light on your situation, but I think it might since you mentioned using fwrite().