If your computer meets the minimum system requirements and you still have the frequent hard drive thrashing and or slowdown, there are a few things you can check for.
First, make sure you have completley defragmented your hard drive. To do this click on Start, then click on programs, then click on accesories, then click on system tools and finally click on disk defragmenter. Within disk defragmenter you will see the option to defragment your hard drive, which in turn will move all folders and files into their appropriate divisions on your hard drive to allow faster seek times and overall system performance.
Another solution you can try is to do the following:
Right click on My Computer and click on properties. Click on the Device Manager tab and expand the "IDE ATA/ATAPI controllers" section. Right click on the "Primary IDE Channel icon and select properties. Click on the Advanced Settings tab and under "Device 0" and "Device 1" TRANSFER MODE select "DMA IF AVAILABLE". perform the following again for the "Secondary IDE Channel" as well.