There isn't a boost 1.35. Some people refer to HEAD as being 1.35 though. Following the instructions on the sourceforge page will get you that.
If you want the 1.34 release candidate however, you can use:
$ cvs -d:pserver:anonymous@boost.cvs.sf.net:/cvsroot/boost login
<press enter when asked for a password>
$ cvs -z3 -d:pserver:anonymous@boost.cvs.sf.net
:/cvsroot/boost co -rRC_1_34_0 -P boost
That should get you it.