I would recommend a dual-processor or dual-core system, using AMD Opteron or the X2 processors; 1GB RAM; some kind of fast disk setup such as 10K rpm SCSI or multiple ATA drives. In the USA you could get something like this for about $900 to $1200 USD.
Reason: you want the dual-processor so that Postgres can be doing something while AOLserver is doing something (as an example); I recommend AMD because they have good memory bandwidth ; and fast disks are useful because when uploading, you first copy to /tmp, then copy the temporary file to some other location (twice the disk bandwidth is needed) .
