I'm a beginner, i come across a problem when using toroiseCVS to download source files from sourceforge, it requires password, could anyone tell me how to get the source files? thanks.
Are you sure you mean CVS and not SVN (aka Subversion)?
CVS is ancient and almost no project uses it anymore! MOGRE uses Subversion and you don't need a password. You will need TortoiseSVN for it. The URL to enter into TortoiseSVN's checkout is "https://mogre.svn.sourceforge.net/svnroot/mogre/trunk"
PS: If you are sure that you meant CVS and if it really needs a password, then you have to ask in the forum of the project whose source you want to download.