Bogus message that start up disk is full

I have a iMac with 2.16 GHz Intel Core Duo, and 2.5 GB of RAM running Mac OS X version 10.5.4.
It has become painfully slow and I get repeated messages that my hard disk is nearly full or is full . I have deleted many files and run the disk utility to verify the disk and permissions and it indicates that the disk in normal. The utility indicates that out of 230 GB , 143 remain available. I have some threads on other forums descsribibng this as a periodic issue occurring occasionally but I have not been able to find any fixes. Trash has been emptied.
Can anyone help me with this? Thanks.

Do you use iPhoto? If you do, when you delete photos, it does not go in the Mac's trash. It goes in the iPhoto trash. You need to empty that trash.

Thanks but I have done that already also. Another poster on a different thread thinks I need to totally reinstall everything after a HD reformat. This would be be quite extreme and I was hoping for a fix short of that. Any other ideas?

Maybe your disk is fragmented? This is usually not a problem for mac users since HFS+ is smart. As a result apple does not include a disk defragmenter. iDefrag is a good option. Contact me if you are interested in iDefrag. it is not free but I know how to get it to work.

A fragmented hard drive may explain those symptoms

Sure I would like to try it. How do I find it? I will do a google search for starters
Carter Newton

I just noticed that several weeks ago when I plugged in my computer in the town home we have moved into, I had joined a local wireless network without knowing it. My ethernet cable was plugged into a modem that was in fact not cable connected. I realized this when I saw a device I was connected to on the finder left panel bar that I did not recognize. I turned the airport off and went through the disk utility routines to repair the permissions, rebooted and I no longer get the variable disk space readouts in the hard disk info dialogue box. My computer must have in some way been trying to associate with another computer elsewhere on this wireless network that I just discovered. Does this make any sense to you nice people who have offered help? Oddly I have a second iMac running also on this wireless network that seems not to be conflicted. Maybe there is a file sharing setting set one way but not on the other?
Carter Newton

Now, an hour later I find that the computer works with a stable indication of the available HD space 150 GB as long as I am not internet connected either by ethernet cable or via wirelsss LAN. As soon as I connect , the problem returns