Firstly, if youre intending on doing professional audio/video recording/editing, youd do well to grab a lot more RAM (Id take it to its maximum of 4GB) and also get a larger HDD (most SATA drives will do, if you jumper them correctly to take them down to the correct speed. Id also recommend getting a nice PCI Sound Card (these can be found relatively cheaply on ebay as these machines are 6-7 years old).
As far as graphics cards go, the built-in one will be fine for basic video editing (Im doing prosumer video work on my MacBooks built-in Intel Graphics using Final Cut Express and it works perfectly). As far as games go, Id take a look at older titles, as many modern titles (such as the Sims 3) are Intel only, and wont run on your G5.