At some point I had both Mercurial and Git installed, and decided it was time to do a bit of cleanup. I have a bias towards Mercurial because it has a better integration in Windows explorer through TortoiseHG (you can call that lazyness).
After uninstalling everything I started clean, installed the latest TortoiseHG version (which btw has a very nice GUI), as well as hgsubversion as explained here: Getting started with HGSubversion
Mercurial was working fine but I was running into the following error each time I tried to clone our repo:
hg clone svn+ssh://myuser@myrepo.com/someotherpath
destination directory: someotherpath
abort: Can't create tunnel: The system cannot find the file specified.
That error message has been driving me nuts for a while, and after trying a lot of things (uninstalling everything, installing Git again, checking library versions ...), I stumbled upon the solution :
set SVN_SSH="C:\\Program Files\\PuTTY\\plink.exe"
As simple as that... Just define that variable SVN_SSH and it worked flowlessly. After that I justed defined it in my user environment to make it persist.
Hopefully this will help someone else.