Duff,
Since you don't specify, I'll assume you have updated to Photoshop 6.0.1 and Mac OS 9.2.2.
What troubleshooting have you done so far? Ran Disk First Aid? Disk Warrior? Rebuilt your Desktop? Zapped the PRAM? Checked for disk fragmentation?
Made sure you have at last 20% of your hard drive space available? How big is your drive?
How old is your drive?
Is your Photoshop scratch disk on your boot drive?
How much RAM is installed? How much RAM have you allocated to Photoshop?
If you are opening files over a network or saving them to a network server, cease and desist immediately. That's a BIG no-no.
See:
Buko "Issues When Working from Networks or Removable Media" 3/23/03 11:02am </cgi-bin/webx?14/0>
and:
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http://www.adobe.com/support/techdocs/19dd2.htm?code=TA>
Copy the CLOSED file from your server to your local HD, work on it, save it again to your HD, close it, and copy the closed file back to the server.