I followed this guide this morning and it worked fine, thanks.
Just to note that you don't need to manually set the LAN IP, subnet etc when you flash over to DD-WRT (step 5).
ipconfig /release
ipconfig /renew
does the job perfectly and saves a bit of hassle.
I'm finding throughput a little unpredictable with this release. My usenet downloads are swaying between 5.5 and 6.1 MB/s whereas on the stock v4.11 firmware I was getting 6.1 MB/sec rock solid. I think I'll flash back for now. Hopefully Tomato will release a compatible version as I love their firmware and find it much lighter on resources (and has better throughput) than DD-WRT.