Doh!! I did that last test on the wrong machine.
I just did it again on the desktop, which I now recall is the one I used when I noticed the problem.
All my browsers on this machine - Slimbrowser, IE and Opera, produce corrupted files if the files are downloaded via ftp within the browser. WinRAR reports "Unexpected end of file" error.
Http downloads are OK and so are ftp downloads with an external ftp client such as CuteFTP.
I can reliably reproduce the problem, but I have no idea about where to start to fix it.
2.6gig P4, 512Mb ram, 80gb hdd with 50 spare, XPhome SP2 fully updated. All browsers fully up to date. PCCillin 2003 fully updated. ZoneAlarm Pro 4.5.594 (holding off on an update there as there were some issues in 5.0.xxx which may or may not have been fixed. I have 5.1.011 stored but not installed yet.)
AA