It was very easy really found a nice guide to help me through it was bit nervous too but it all went fine let me try and find that guide as it was easier than the instructions on DD-Wrt page...
http://samiux.blogspot.co.uk/2010/03...-wr1043nd.html
Make sure you get the latest version from the DD-wrt forum too as the one shown on the main page is quite old..let see if I can find it ohh seem there been a new version released just the other day will have to flash that later..
ftp://ftp.dd-wrt.com/others/eko/Brai...-08-12-r19342/