RAM upgrade 
Upgraded the Dimension 5150 to 4x1GB sticks. There are two problems resulting from this:
- Linux only sees 3.3GB (3365780 KB according to free)
- the external 3c905 card I installed in it no longer works (the computer is now complaining:
PCI: device 0000:03:02.0 has unknown header type 7f, ignoring.
...which I presume is related to the now-inaccessible 3c905.
Also discovered that the 80GB disk I installed in anticipation of gratuitous VM activity is busted:
end_request: I/O error, dev sdb, sector 65
Buffer I/O error on device sdb1, logical block 2
ata1: translated ATA stat/err 0x51/40 to SCSI SK/ASC/ASCQ 0x3/11/04
ata1: status=0x51 { DriveReady SeekComplete Error }
ata1: error=0x40 { UncorrectableError }
scsi0: ERROR on channel 0, id 1, lun 0, CDB: Read (10) 00 00 00 00 42 00 00 01 00
Info fld=0x42, Current sdb: sense key Medium Error
Additional sense: Unrecovered read error - auto reallocate failed
Better now that a week from now when I'm running something on it, but still.