presuming that you have used the kde window manager/environment which is default with mandrake, you could go into the the kde control centre (configure my desktop) then system>login manager>users, then you'd have to hit the "administrator mode" button at the bottom of the page, which then request's your root password, which you enter and let it do it's thing, you'd then normally have the login manager with a red border, which enables you to uncheck the box that makes root a hidden user.
After log out/log in you should see root as an option to log in graphically.
As far as viewing the /var/log file with CLI, it's not a problem. You'd just open a terminal/konsole and then "SU" (no quotes) and enter, then apply the root password.
From there, just to view the /var/log/boot.log you'd then just type
at the # prompt and use the arrow key's to look at the file. When you've finished you can either just close the terminal or do it properly and type :q (yes you do need to type the : colon).
Just for info, the code example I've quoted, opens the /var/log file in the "VI" editor, it may be prudent to have a look around for proper instructions on using VI it's a very competent editor.
Though if you don't like the idea of using that yet, once you can log in as root graphically you can just search through konqueror for /var/log/boot.log and then do the right click thing and open it with "other>more applications>editor's>kwrite" which gives you an editor pretty much like a word processor, you just have to remember to save it and close the file if you'd made any changes, which I doubt with /var/log/boot.log (the same thing in VI would be :wq)
p.s. I thing my explaination is correct, though with my system it's a little different as I have a seperate /boot partition and usually have to have it mounted as I'm set up that it is only mounted during the boot process, but the above "should" work.