Nod32 is one of the better a/v's on the market and has a small footprint.
But it keeps getting beaten by that damn GDI32 virus.
Every antivirus will have a low point.

And besides, I said it was one of the 'better' a/v-s on the market ... not 'the' best.
And btw, seigezunt ... if you want a comparable antivirus with antispyware for which you don't have to pay a thing (aka free software), look into Microsoft Security Essentials.
I switched to that because it beats the ones you have to pay for, offers highly effective antivirus and antyspyware (high detection rates), and keeps a minimum footprint on the system.
I'm running Windows XP SP3 on a Dell Vostro 1500, Intel Core 2 Duo cpu T7250 @ 2.00 Ghz
Not bad.
You know ... your system is already decent.
You can easily get away with upgrades to your RAM, CPU (if you want to) and HDD if you want to bring your laptop up to speed (along with a clean Win 7 64bit install).
As far as I can tell, your computer can support up to 4GB RAM (PC5300 at 667MHz) - DDR2.
One thing occured to me that could be related to the slowdowns you experienced.
When was the last time you cleaned out the air vents on the laptop?
The simplest thing would be to temporarily unscrew the lower panel (while the laptop is unpowered and battery removed) and vacuum the area (the cpu fan area especially since dust builds up there a lot).
Also ... while you are there, you could probably unscrew the cpu fan as well, put it to the side (not unpluging the wires that connect it to the mobo) and clean out the dust that built up at the base of the airvent - I found A LOT of it there in numerous systems).
I recommend cleaning out the air vents once every 6 months, up to a year (depending on how dusty the area you live in is).
Your chipset is PM965 (Montevina Platform) from what I can tell in the specs (you can double check with a free program called CPU-Z), so the FSB should be operating at 800Mhz.
That means you can get a T series CPU operating at 800Mhz FSB ... such as T9300 (bear in mind that it also comes in 1066Mhz FSB versions ... so you will have to make sure the CPU's FSB is at 800Mhz).
One thing to keep in mind though would be that the T9300 is made in a smaller manuf. process (about half as small) and operates on 2.5Ghz (on each core) which also translates into practically identical, or much lower heat emission than what you have now on maximum load, but it's also a bit costly as a result (close to $250 on ebay if I'm not mistaken).
Though I suppose you can look into some other T series cpu's that are faster in comparison to yur current one.
Truth be told though, for what you do, I think the current cpu (T7250) is juicy enough (and it's also 64bit, so you can safely install Win 7 x64).
As for the HDD ... right now (if the online specs are accurate) you have a 160Gb Seagate Momentus.
I would recommend you go out and buy a Hitachi hdd for your laptop (2.5" one of course).
A Hitachi Travelstar 500GB at 5400rpm (which has more layers and translates into more speed compared to other 5400rpm drives) would cost around $60.
Or ... you can get a Hitachi Travelstar 320GB at 7200rpm for around $80 (these prices are from newegg btw).
So focusing on the RAM (4Gb) and a better HDD would be something worth looking into if you want to bring your computer up to specs a bit (and a 64bit OS) ... and cleaning up the dust inside the laptop.
I think you would spend in total around $140 to $160 for those 2 upgrades (RAM and HDD).
One final thing ... you can also undervolt your current cpu to consume less power under maximum load which would translate into even lower temperatures (and no, this would not bring down the performance since we are talking about finding the lowest stable voltage at which your cpu can run at 2.0GHz) and extend it's lifespan even further.
I did the same with my cpu and gpu ... managed to bring down maximum temperatures by about 15 to 20 degrees Celsius - plus I overclocked the gpu under lower voltages by about 25% overall and still get same low temps with increased performance in games and 3d Studio Max).
I know, it's a lot to take in at one time. I'm just giving you options on what to do with your present system that would likely save you the overall hassle of spending a lot of money on a new system, especially if the present one is far more than salvageable.
What you decide to do is your call though.
P.S. I don't know how much you know about computers overall, so I apologize if some of the detailed info was 'baby talk'.
