In the long run I'd buy the replacement disc, although I would instead recommend upgrading to Office 2008 which will be more compatible and will not require Rosetta to run a PPC application. Since you have the ability to use an academic purchase the upgrade isn't that expensive.
As for transferring what you have just copy the applications folder, the items in Applications Support, and the preference files. There are two Applications Support folders. One in the /Library/ folder and one in the /Home/Library/ folder. Preferences are all in the /Home/Library/Preferences/ folder.
It really doesn't matter if you make the Office transfer before or after upgrading to Snow. Before upgrading be sure you do the following:
1. Repair your hard drive and permissions.
2. Disable or remove any third-party utilities such as contextual menu items, preference panes, Internet plug-ins, and input managers. These may not be compatible. I would suggest disabling any login items as well.
3. Make a bootable clone of your existing system to a freshly formatted external drive.
4. Perform the Snow upgrade.
You can then test your third-party utilities for compatibility. You should quit all running applications and disconnect all peripherals for installation. Ideally you should boot into
safe mode for the installation.
You do not need to follow these suggestions, but from my extensive experience these precautions are most likely to assure a trouble-free upgrade.