If you install Linux Mandrake 8 i believe you can resize your windows partition without losing the data on it... plus the install is self-explanatory.

In fact, mandrake 7 and 7.1 have that feature as well... and all versions of Linux should come with a DOSTOOLS directory with a program called FIPS which will (if i recall correctly?) resize your partition without loss of data!

If you want a step-by-step Linux installation instruction, I suggest you either buy a boxed version of Linux (come with manuals therefore install instructions) or download the instructions from the distribution's web site, e.g. www.linux-mandrake.com

Hope that helped!