Are you talking about copying the Windows image or the Mac image or both? I don't use Parallels, but I use bootcamp. In the bootcamp world you would have to run bootcamp to partition the drive so that it installs the boot record stuff. I think that code is outside the normal volume area that is affected by normal disk copies and imaging. Once the partition is made, you can restore a Windows volume using Disk Utility (I have done it).
As for the Mac volume, I assume that you know that if you have different versions of OS X you will have plenty of headaches copying files from the old computer the new one (because some preference files have new names or locations, and there are other program changes). Assuming the two computers are of the same OS version, you could try installing a G5 image on a new iMac, but I wouldn't have very high expectations because the lowest level programming has to be in a native code for the CPU before the OS loads the universal code libraries.
This might be a good opportunity to start from scratch and install only the programs that you really need onto the new computer and leave the old mystery programs on the old computer. Plus you start with a less fragmented drive this way.