Q: How to upgrade PowerBook G4 1.67Ghz to 10.5.8?

The Combo update for Leopard 10.5.8 should be all you'd need to update

an OS X 10.5.x from any step to the last update step; as that had been

a consolidated Combo to include earlier fixes & patches. Then, after a

Combo update, restart, repair disk permissions in Disk Utility, than then

run Software Update again.

Two things, one is: compatible quality RAM tested on Mac computers

and specificially for Macs running OS X. Secondly: hard disk drive free

or unused capacity, since OS X in a PowerPC relies on Virtual memory

that's free space used as swap file temporary read-write system memory.

Sometimes, the applications + OS X need more RAM than is physically

possible to install; and it may not use what it has efficiently.

•Problems from insufficient RAM & free HDD space:

http://www.thexlab.com/faqs/lackofram.html

•Freeing space on your Mac OS X startup disk:

http://www.thexlab.com/faqs/freeingspace.html

This is slow enough, so if the hard drive has little free space and not

necessarily in a large block, the OS X has to hunt and find the scattered

places it can use to write temporary VM files to. At hard drive rates of

speed, so that is also slow.

•Mac Performance guide - thesafemac:

http://www.thesafemac.com/mpg/

•The X Lab: X-FAQs:

http://www.thexlab.com/faqs/faqs.html

Do you have an externally enclosed hard drive in FW400/800 case, with

its own power supply? With oxford-type chipset... suitable for OS X clones?

You could clone the system to an external, if you may want whatever is on it,

then be sure it is a bootable clone by starting up the Mac from it; then go in

and erase/install (over-write drive at least 7-pass) to test the HDD and see if

it really should not be replaced with a new one. HDDs fail after a shorter time

span in a portable, than a desktop. Yet new models can fail in short order.

If temped to try an SSD, see what OWC has in the way of Legacy SSDs for

older portables, as they are most compatible with the hard drive data rate

and the ATA/IDE (PATA) specification. Certain rules tend to apply to using

a solid state drive, instead of a platter & styli hard disk drive.

Hopefully if you have the original grey-label install-restore disc DVD set,

you could run the Apple Hardware Test on the bootable disc, to see if

there is any hardware reason why it could be acting up.

Check to see if there are any "previous system" folders in the Mac,

since they can't be used to run it, but they do take up space... Trash

old previous user-created content, but not system parts, if the HDD

capacity is near too-full. See the link above about freeing space.

Checking Console (utility) for Clues:

http://www.thexlab.com/faqs/checkconsole.html

Not sure what else to say...