Secure File Upload

[Tom Hukins]

Given that several people here run various Web sites, I'm hoping
someone can point me in the right direction.

I host a few Web sites on a Unix box and so far I have copied files
there using scp, or edited them directly on the box.  That works well
for me.

I now want to let a semi-technical person upload a site from a Windows
XP box.  Fine, I thought, I'll create a new account and provide SFTP
access, pointing this person (who has used FTP before) to WinSCP.

Unfortunately, with this approach I can't prevent SSH logins easily,
and I can't restrict access to a subset of the machine's file system.
Ideally, I'd like to do both for security reasons.

I could faff around with chroot and run separate services, but as I
only play at sysadmin in my spare time, I like to keep things simple.

Running WebDAV over https within Apache might do the job, but WebDAV
feels like a heavy protocol and I've seen XP play with it badly in the
past, admittedly around 5 years ago.  Also, to keep everything
encrypted, I need to give the server a certificate.

Thinking backwards, I guess I want to:
1) Make the process as easy as possible for the uploader
2) Reduce the risk to my system, should the account become compromised
3) Reduce the chance of making the account compromised (encryption)

I suspect some sort of ideal solution may not exist, but I would
welcome any thoughts, insight or creative workarounds you lot might
come up with.

Tom