If you're going to symlink directories (which should work for any posix systems, not just linux), I'd suggest that you make a perl5.8 directory, and not name it 'perl5', as any perl 5.8.x modules with compiled components are not backwards compatable with 5.6.x and earlier. (and the 5.6.x modules with compiled components aren't forwards compatable with 5.8.x)

Update: ah...if it's the binary that's in the location (I saw 'lib', and thought it was the module include path), then I'd definately suggest being careful with messing with the original installed by the OS. See Re^2: Solaris, Perl 5.8 and use 5.005 and Maintaining an Enterprise Perl Distribution for more details.