hey sqlserver2k8 is a katmai verson or i thing beta version
so dont intall if u want to intall then same procedure as sql server2k5.
Run Katmai select dx like 64, 86, itanium whatever
click on intall then select item to install by default it intall .netframework, windows installer and workstation books .
click on next select sqlserver and workstation online books
click next then use default instance then select local network then click next,select mixed authentication click on next, next finished
ur katmai will successful installed
regards
Lucky