How can I speed up imac

See the OWC site at http://eshop.macsales.com/shop/apple/memory/iMac and it will tell you what you can upgrade for your iMac. Often you can upgrade more memory than Apple says.

See this FAQ on improving performance: http://www.thexlab.com/faqs/performance.html

Ensure you have a bunch of free disk space for operating systems usage. WIth a 2TB drive, you should.

You might download OnyX and run the tasks on the cleaning and maintenance tabs: http://www.titanium.free.fr/download.php

Look at your login items and those listed at the bottom of the System Preferences window to ensure they are the 10.6 versions.

To determine if you can use more memory for what your run, bring up the Activity Monitor (on your hard drive in applications/utilities). On the system memory tab look at page ins and page outs. If page outs is 10% to 15% or greater than page ins, you can use more memory. A page out is when the system writes memory to the hard drive, to make room for something else to run. Too much page out activity can slow the system down. In a perfect unconstrained memory world, page outs would be zero. They reset when you reboot your system, too.

Memory aside, if the performance of the system is OK, then that's an inexpensive upgrade. However, if the feel to you is slow and encumbered, then perhaps a new system is a consideration. Another option would be to install an SSD in place of the hard drive. That will make disk operations uber speedy.