The easiest thing that is free is a fresh install of Windows, if possible, don't use the restore disk. Make sure you eliminate all the extra HP junk/drivers, that aren't necessary, and use something like RegEditor, to clean up your registry, and elminate unecessary files.
Try to pretty much only run a firewall, running a virus scan all the time, pretty much does nothing but slow things down. I only open my virus scanner to check new disks, that come from other people, before I use them, and to scan downloads. Having it continually scan your hard drive files for viruses slows things down.
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