OS X :: Finder Works Slow On Leopard ?

I had problems with Finder, it just crashed on me when I opened folders that had a bit more files. I have an 24" iMac with v10.5, 2.4 GHz Intel Core 2 Duo, 3GB 667 MHz DDR2 SDRAM. I bought it a year ago, add a month or so... So after I got all the glitches with Finder, I transported Applications, Documents, Music, Pictures and some other folders on my desktop to an external Hard Disk, when I finished with ERASE & INSTALL, Finder doesn't crash, but it's VERY VERY slow, for example, in my iTunes Music folder, I have about 560 folders, and when I click SELECT ALL(on the keyboard) it stops for maybe a minute or so, and then I try to copy them to a folder, when i try to drag them, it stops for 2 minutes or so... I haven't even copied much from the external Hard Disk. Except going back to Tiger, is there any other way, because my iMac is...not new, but not old enough to have those glitches... PLEASE HELP ME, this isn't the first time, this is actually my 3rd time doing a reinstall, 2 ARCHIVE AND INSTALL's and 1 ERASE AND INSTALL... what could it be?