Hi
Is the hard drive running in DOS compatibility mode? Right click My Computer anbd select properties, click the Device Manager tab, drill down into disk drives then selct the relevant entry. If it is running in this mode your computer will c-r-a-w-l along.
To fix it, try renaming your config.sys and autoexec.bat files so that DOS drivers don't load, if this does not fix it search for the following TechRepublic article:
Solve MS-DOS Compatibility Mode problems on PCI IDE controllers with these troubleshooting tips
Also, make sure you only have the required network ptotocols installed - too much traffic can slow things down. Has the drive been compressed? I experienced a severe reduction in performance on a machine once after it was compressed.
Also, make sure that the Temp and My Documents folders are not filled with loads of files. If so, create new folders off My Documents and redistribute the files.
Good luck.