Here's how I do it:
download the latest source snapshot from
http://inkscape.modevia.com/svn-snap/?M=D atm it's 22070
Open terminal, it should open in your home folder automatically. Commands in terminal are executed one line at the time, type the command and hit enter, wait till you get the prompt back.
I created a special folder called inkscapedev to hold all my dev installs (you don't type the $ sign, just what's following):
$ mkdir inkscapedev
Go into the newly created directory:
$ cd inkscapedev
unzip the downloaded file here (you need to type the path to that file. If you're confused just copy the file into inkscapedev folder using your usual file browser and use exact command from bellow):
$ tar jxvf inkscape-22070.tar.bz2
Go into the unziped folder:
$ cd inkscape-22070
Execute autogen script:
$ ./autogen.sh
Don't mind the message you get to make install now, you need to to something else first - make folder named build
$ mkdir build
Go into the newly created directory:
$ cd build
Execute command (copy it from here):
$ ../configure --prefix=`pwd`/../install
Execute command:
$ make install
This one will take a very long time, maybe an hour, wait for it

When it's done you can launch it from the path /home/[your home folder]/inkscapedev/inkscape-22070/install/bin/inkscape. The easiest is to create a new launcher, right-click on the desktop and choose Create launcher, type Application, name Inkscape22070, command /home/[your home folder]/inkscapedev/inkscape-22070/install/bin/inkscape
Good luck