You could do it yourself, but it probably won't matter.

Ever since Apple introduced Lion (OS 10.7) and now with Mountain Lion (OS 10.8), the Mac operating system no longer will use Power PC-based programs. It is a virtual certainty that the programs running on your G5 are all PPC based. You can check this by clicking on the application icon once, then going to the File menu and selecting Get Info. In the General portion, you will see a listing for Kind. If it says Application with nothing next to it or a PPC, then it is old-style software and won't run. If it says Universal or Intel, then you might be able to use it on your new machine, but will probably still need to be updated to some degree.

Find the installer discs for the ones you can use and see if you can update from there, or just get the latest version from the software manufacturer.

So rather then go through the expense of having Apple do it with a One-To-One membership (which does have other advantages) or doing it yourself, just to find out the programs won't work, bite the bullet and upgrade your programs. Instead of doing all of them, take a look at what programs you actually use on a regular basis and concentrate on those first. The rest of them will present their needs when necessary.