Its not allowed, ripping the CD/DVD to play on the HDD via emulation software is circumventing the games security protection like SecuRom.
The game will prompt you for the correct CD in the drive anyway.
If you wish to keep your room free of CD/DVDs keep stored somewhere. Or get steam and start buying your games from the online store and download the games digitally to your HDD.
www.steampowered.com