I don't think 9i Personal Edition is yet commercially available.
I guess you would need minimum of following recommanded configuration.
1) IBM compatible PC.
2) Intel PII or higher (min 233mhz) CPU - No celeron.
3) 128 MB or higher RAM.
4) 2 GB free space.
Hope this helps. For acurate information visit technet.oracle.com and search for 9i.