Power Mac G5 Dual 1.8 PCI (4 RAM Slots) - want to upgrade to 8GB?

If there is not enough RAM, OSX will use space on the disk drive, so the amount of RAM should not limit the file size an application can handle, but speed will be reduced. 32-bit addressing can restrict the use of huge files, but there are ways that applications can get around it (at the expense of lower speed).

If After Effects has a file size limit, extra RAM will not help A later version (maybe using 64-bit mode) may handle larger files. 64-bit applications can be written to run in Tiger on G5s, but will be easier to write when Leopard is released.

You may be able to use some other application, such as Photo Shop, or Graphics Converter, to extract part of the TGA file, or reduce its size by changing its resolution, so you can use the result in After Effects.

4GB is a REAL hardware limit in that G5 motherboard ( 4 DIMMs max, 1GB max ). OS X ALWAYS has VM turned on, so overflow goes to disk ( slooooow, watch the pretty beach ball spin and spin ) ).

Are you sure After Effects can handle such a large file, even if you had 8GB RAM? If not, upgrading won't help.

After Effects can import and render a file with a maximum of 30,000 x 30,000 pixels, so all the RAM in the world isn't going to help you open that file.

And even if you could install more than 4GB of RAM in your system, AE will not be able to address it all. AE 6.5 could address 2 GB of RAM (IIRC), AE 7 bumped that to 3 GB, and AE8 (CS3) bumps it to 3.5 GB.