Will Norton Antivirus 2009 bog down my computer's performance, just as Norton

[bgsimsrvp]

Internet Security 2009 does now? My computer has a 3400+ AMD Sempron Processor, 256MB of memory, 100GB hard drive. It runs very slow with NIS 2009. I have been offered the option of downgrading to Norton Antivirus 2009. But will my computer run any faster with it?