Just thought I would post this in case anyone else out there is interested. I was using Norton Anti-virus, but found it cut the performance of my older machine down dramatically. This AVG software is free, and has sped up my old 600mhz celeron machine significantly. Anyone with an older machine like mine has probably noticed the detrimental effect on performance of Norton Anti-virus. This is a free alternative, that works well.

Grisoft AVG download