virtualbox.org

Hi,
I get 2 iso files below, for Win 2003 server.
en_win_srv_2003_r2_enterprise_with_sp2_cd1_x13-05460
en_win_srv_2003_r2_enterprise_with_sp2_cd2_x13-68584

do I need to combine both into one iso for being able to set it up in VirtualBox? If I only select the 1st one, I cannot proceed with the setup.

Do the same thing you would if you were installing on a physical machine. If the supplier tells you these ISO files need to be merged, then merge them. Generally however a 2 CD set needs to be installed by putting CD-1 in the drive, then let the installer run until it prompts for CD-2. If that isn't how it's done then best ask the supplier for installation advice.