D620 choppy video, general slowness after clean install of XP Pro

Hello,

I recently did a clean install of Windows XP Professional on my Latitude D620 after having a recurring issue with viruses [despite having a good anti-virus service (proof positive that no anti-virus service is perfect.)].

I have since experienced choppy video playback when using the Internet (regardless of browser, regardless of file format, regardless of YouTube or other) as well as general slowness when scrolling down a webpage, or waiting for a webpage to load completely, particularly when a page has many advertisements (e.g. a newspaper site).  

I am not missing any drivers, as there are no 'question mark' icons on the driver page.  I have also installed Flash, Shockwave, and Java, so I'm not sure what I could be missing.  

I don't believe that it is a hardware problem because, despite the persistent virus that prompted the clean install, I didn't have any problems prior to this.  

The only thing that I did differently with regard to the clean install was to create a partition that did not exist before; 15 GB for (C:) for the operating system and applications, and approximately 40 GB for (E:) for my files.  I also changed the location of 'Temporary Internet Files' to (E:) drive.

I would appreciate any suggestions.  Thanks.