Desktop running sooooo slow

My Mac desktop is about four years old. For the last few months, it's been running really slow. Slow to open Microsoft files, itunes, even when surfing the web.

Can anyone offer a suggestion for what I could do to speed it up?

A simple first step would be to install OnyX and run through the tasks set in the Automation tab. Second, check how much disk space you have free. You should try and aim for about 15% at a minimum.

What are the specs of your machine?

Here's what I have:

Processor Name: Intel Core 2 Duo
Processor Speed: 2.66 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 6 MB
Memory: 2 GB
Bus Speed: 1.07 GHz

Where can I see the percentage of memory used?

You can see how much free space you have in the status bar of any Finder window. If you don't see the status bar, go to View > Show Status Bar.

Memory ≠ storage. Don't confuse the two unless you want to confuse everyone else about what you are talking about.

Memory is synonymous with RAM.
Storage is synonymous with hard drive space.

Looks like the capacity is 274.88 GB. Available 17.43

chas, thanks for the clarification. What info could I give you for advice?

That's only about 6% free which is much too low. Try and delete some content or better yet, move some of the content to an external hard drive.

Just crept up on me I guess. I do have a lot of music files that I could put on an external. What else are the big memory eaters?

Your hard drive free space availability is falling into what I would consider the danger zone (ie you're well below 10 percent still available). So clearing up some space would certain be one thing I'd suggest.

Another is to get in the habit (if you aren't already) of actually quitting (not just "closing") apps when you're not using them. They relaunch very quickly these days so there is no reason to keep to them open unless you are in fact using them continuously. I find that a lot of people don't realise that they haven't actually quit their apps and there they all are, still open and taking up RAM and resources.

Another factor I should have asked about in my previous post: how much crap are you storing on your desktop? This can slow down the machine quite significantly if the amount is very large, so I usually tell people to avoid keeping things on the desktop except for very temporary purposes. There are a number of good reasons for this "best practice," I won't go into them all here, but I have occasionally seen very dramatic results when people clean their desktops in terms of Finder responsiveness.

Vansmith touched on other good suggestions, and you might also want to consider a RAM upgrade (though that would not be a "fix" for these issues). 4GB is better than 2GB going forward, and RAM is pretty cheap and easy to install on an iMac.

RAM is definitely something to consider if the cost is feasible and you feel comfortable installing it (or know someone who is). chas is correct - it doesn't fix the habits but it can give you some room to do a little more with your machine.