Q: SLOW since upgrading to new os a couple of weeks ago. I also changed my modem and yesterday upgraded to Office:mac 2011-is this more than my computer can handle? I get the spinning disc even when I close an application??

How much RAM and how much hard drive space available?

Another question - is 10.5.3 what you had or what you upgraded to? Office 2011 minimum reqs says 10.5.8.

When you click on the apple on the menu bar, and about this mac, how much memory does it say your system has? Mid-2007 iMac came with 1GB memory standard, which is the minimum for Snow Leopard. That could be contributing to the performance if that's how much memory you have.

See these FAQs which may help:

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

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

Snow Leopard really needs a minimum of 2Gb of ram to operate well. Yes it can run on less but performance will be sluggish. Also Web browsing requires more ram now than it did when you purchased your computer. If you use the latest version of Microsoft Office it also requires more ram. I recently upgraded my 4 year old iMac to 4Gb of ram and it is like having a whole new computer. It opens programs quicker, shuts them down quicker and web browsing is  much quicker.

Upgrading ram is inexpensive, certainly less than purchasing a new computer and in my opinion, based on my experience, is well worth it. I would upgrade to whatever the max is or 4Gb if your Mac can handle that much.

You can do ram upgrades yourself. It is easy. Most Imacs ram slots are on the bottom frame of the monitor. Check your manual or go to here :http://support.apple.com/manuals/#desktopcomputers to find the appropriate manual which will include instructions. It is really easy to do.

You can replace the memory yourself, no need to go to anyone. See this Apple note on how to: http://support.apple.com/kb/HT1423