There are numerous ways: Using an Ethernet cable between the PC and Mac, another involves Ethernet cables from each computer to a router, then there is wireless, perhaps a Firewire (if the laptop has one, or a Firewire PC Card installed) and / or USB hard drive; and, even using a RAM Disk (thumb drive, USB storage device).
What really helps those offering to help - is being provided specific information. Such as the model name / number of each computer (Ok, G5 does help; but, 'old Dell laptop does not'), Listing the type of connections on the laptop is essential. Do both computers have wireless capability? Knowing the size of the laptop's music library folder would also be helpful.
You may be able to copy the laptop's music library folder contents, in steps, by using a USB storage device (while some in the 4 GB range are available, the most common sizes are 256 MB, 512 MB, and 1 GB). Copy only the songs, no folders. Drag them from the USB storage device onto the G5's 'iTunes' window. This way they will be properly placed and labeled. The labeling part will only happen if the G5 is connected to the internet.