Ok, from this i can only suppose it is a POWER3 machine. Have a look at the housing to find out the model. If it is a desktop system it could be a 42T, a 43P or something such (42T was a Microchannel system, 43P a PCI system). If it is a deskside system it might be a F30 (Microchannel) or F40 (PCI). The system must be at least 11 years old.
On the older systems there was usually a grey "sticker" with a big IBM logo on it and (in small writing, below) the model type.
Here is a picture of a 42T, on the right upper edge you see the said sticker:
http://www.logicprobe.org/systems/42t.jpg
I hope this helps.
bakunin