Thanks for the tip. I'm currently using SourceAnywhere for remote access in our China office which has a caching server which massively improves the performance over the high latency connection. I'll have to check out the command line for SourceAnywhere and see if it has a similar function.
I was thinking of ditching SourceSafe and moving to SVN, but I haven't tried SVN between China and the UK yet so I'm not sure that the performance will be good enough...
