You're right about upgrading the SGI 320 to PIII 600Mhz, but only using the older Katmai PIII processor, you can't use the newer Coppermine PIII. Also remember that the bus speed for the SGI 320 is 100Mhz, so get the PIII with the 100Mhz front-side bus. Before installing the PIII, though, you will need to upgrade the PROM using a package called the Supplemental Software Kit (SSK). Go to SGI's SSK for Windows web page (http://support.sgi.com/nt/win2k/index.html). This page has the intructions for upgrading the PROM using the SSK package and has the link for downloading the SSK. Even if you're not using Windows 2000, this updated PROM works with Windows NT and contains support for the PIII 600Mhz. When you download the SSK (size 18.5Mb), run it and only choose to create firmware floppy disk (the other choice is only if you're using Windows 2000). You will also need an available blank floppy. Read the intructions on the SSK page for further details on the process of upgrading your PROM.
Another thing you will need to do is adjust the jumper settings on the motherboard. The SGI 320 user manual will pinpoint the location of the jumpers that are used to confirm the speed of the processor. For your current configuration of a PII 450Mhz, the jumper settings are: up,down,down,up. The correct settings for the PIII 600Mhz are: down,down,up,down. These settings work for single or dual cpu configurations (a different jumper on another place on the motherboard is used for confirming single or dual configurations).
*If the system you're going to purchase doesn't come with a user manual, you can download a pdf copy from the following link: http://support.sgi.com/nt/product/320/
As far as the memory goes, the maximum you can put on a 320 is 1GB of RAM. The 320 has two banks (A and 
capable of holding a minimum of 128MB per bank or a maximum of 512MB per bank, for a max total of 1GB. You stated that the system you are interested in purchasing already has 256MB of RAM in it. This could either be in configurations of 128MB in bank A and 128MB in bank B, or 256MB in bank A only. If the former is the case, you can't upgrade the RAM without removing the memory already there. If the latter is the case, you will be able to upgrade to 512MB later on, which is plenty for most 2D/3D apps.
One more thing, you didn't state whether that system has a SCSI card/hard drive. If it doesn't, one thing you should note is that if you want to put a SCSI hard drive in it and use it as a boot disk, you are limited to the Qlogic SCSI controller cards. This isn't neccessarily a bad thing, but the 320 recognizes only the Qlogic cards for boot devices. The 320 can still use other SCSI cards for secondary (non-boot) drives and/or other peripherals, but not to boot your computer.
LORT
