...by going to control panel/system/advanced/performance settings and then selecting "adjust for best performance". This will turn off all the basically useless but resource-hungry XP visual styles and graphics and revert the system to "classic" (Win 2000 and earlier) video settings. I have a 2 gig RAM iMac and this has improved things significantly.
There's something ironic about a performance enhancing selection that responds with "Please wait" . There is far more one can do to improve performance, not the least of which is to disable any unneeded services (indexing comes to mind). There have been a few threads started here and are probably still available for browsing.
My Windows XP installation is through Boot Camp, and had a lot of stuff enabled like Trillian (a multi-service IM program similar to Adium) and Skype. Now that I am booting to Windows through a VM window, I don't need two copies of these programs running. so I disabled the "load with Windows" option. Windows boots a lot faster now. I can't delete them from the system, in case I ever have to boot into Windows I might still need those programs, but disabling unnecessary services is always an option. Having a simple background helps as well - a photoquality background takes up system resources and slows down the refresh. If you're never going to use certain applications like Outlook Express and the Solitaire games, you can remove them through Control Panel -> Add/Remove Programs -> Windows Setup. They don't save much on resources, but you'll get some disk space back. -Z
