What is your machine's model number, it will help me find what parts you can use in greater detail? If you still want it to be a mac, I would recommend the following:
Change the original hard drive with a 7200Rpm IDE drive (which you can get in sizes up to 400GB)
upgrade the ram, Apple says that the max is 1GB but it will actually will support 2GB
put in a new DVD burning drive, you need an IDE drive and you can get up to a 24X DVD burner.
You can install an airport wireless card, depending on your model, you can get either an 802.11b AirPort card or an 802.11g AirPort Extreme card.