Why is the latency on my computer much, much higher since installing F-Secure internet security 2007?

Since installing F-Secure internet security 2007, my Windows 2000 systems’ responsiveness to clicking buttons etc seems to be much higher, especially a few minutes after resuming from hibernation.

The total ram usage on the machine has increased to 313/512MB.
The hard drive is quite slow, ATA-66, Maxtor DiamondMax 32049h2.

Using the system monitor, I am not noticing any spikes in % CPU Time, RAM Pages/Sec, Page faults/Sec, % Disk time while this laggyness is occuring.

I wonder if its something to do with hardware interupts becuase I know these can cause spurious problems, and it is possible that the onboard networking was being used to update F-Secure when it was laggy . The computer is a Compaq Evo D500 sff with NVidia Vanta LT AGP graphics (latest drivers).

Any ideas/suggestions appreciated!
{THIS IS A *WORK* MACHINE.
2GHZ P4 512MB RAM. HDD’S SLOW.
Why upgrade, it works fine with W2K. I hate the notion of Vista.}

*IT’S THE CLIPBOARD, WHENEVER I COPY ANYTHING (text when I realised), IT SLOWS TO A CRAWL.*

I’ve gotta work on eliminating some variables, any *REASONABLE* suggestions appreciated.