defrag fat and ntfs volumes

I do a lot of graphics with huge files on my stand-alone workstation. Over the last couple of months the system has slowed significantly with the hard drive churning and churning endlessly.I was always under the impression that ntfs volumes could not be defragged but a OEM tech sup person says yes and there are utilies out there to do it. is this true and if so where can I get a defragger for FAT and NTSF volumes?. Running dual 600meg pentium3’s with 256meg of ram. Thanks for any help.