I currently own parallels 3.0. Is there a way for me to install a trial version of 4.0 over my 3.0. For example I just want to upgrade my 3.0 version as a trial without having to install a new operating system again.
No, you can't install Parallels Desktop 4 without downloading the installation package, but you don't have to install a new operating system either. Here's what you should do:
-back up your VM (copy the ***.pvs and ***.hdd files somewhere safe). also make sure you have axed Parallels Tools v.3/any anti-viruses/security software you may have installed in your VM
-install Parallels Desktop 4 and upgrade your VM. see if your game runs fine under the new version
-if it does, enjoy. if it doesn't, uninstall version 4, install your old version 3, get your backed up VM and copy it into the defaulr folder