I persevered late into last night with Buildroot. Eventually I was able to get the make to finish. For it to make the toolchain, uClibc, BusyBox, Linux, and the root JFFS2 FS :)
Reflashed the root FS and zImage to the VCMX212 and tried booting. At first I was getting lots of MTD error messages. After a few boots (usual to init the JFFS2 FS) I managed to get to the BusyBox prompt :)
Unfortunately it is very unstable :( Likely to be issues with MTD. A quick google trawl before bed shown lots of MTD issues with various kernels.
Today I'm going to start afresh with Buildroot and fill in any missing gaps in the Wiki page.
Then on to start looking at the MTD problems...