It's building itself beautifully now, thanks div! I had tried yesterday to track down alternative sh.exe but had trouble finding ones that would work with your build system (cygwin's acted really weird, for example).
edit: Spotted a bug but it's an easy fix. If you just extract the build folder exactly, something (I think make) chokes because of the spaces, though renaming it to something without spaces lets everything compile correctly. e.g. I had extracted it to e:\Nexuiz SVN Compiler but the batch file died with an error "e:\Nexuiz is not a valid command"
This could only be filesystem specific though since no one else seems to have had trouble with it and the partition I'm running it on is ext2, not ntfs or fat32