[Serna] File locking/versioning with Serna -- what are others using?

Hi

We have 5-7 editors working collaboratively on XML documents.  
I maintain WebDAV folders from Apache because that was the 
"easiest" way of getting a file lock on our XML documents 
with Serna.  I am having frequent problems with WebDAV file
locking, however, and it has turned into a lot of annoyance
 for the basic protection of a simple file lock.

Beyond a basic file lock, a versioning system could also
 be useful for us. It would be very helpful to know what 
others use either for file locking or versioning in 
similar environments.  To suit us, it should be friendly to
non-technical users.  Our setup is a handful of XP 
machines in a Windows server domain.

I've had Subversion (with TortoiseSVN) recommended to 
me and I'm researching that, though without much past 
experience of versioning systems to compare against.

I'd be grateful to any Serna users who could offer 
advice or comments on file locking / versioning 
systems they've got working well with Serna.  
Even if all you have is a simple file locking mechanism 
that works reliably, I'd be interested to hear what 
it is.

Tim