You will have a bad experience running Windows 7 on that old laptop. Most VGN AR models have a 2 gig ram limit for the motherboard. Best thing you can do is get rid of Vista and install XP Home Edition. XP uses less RAM than Vista and a lot less buggy. Get XP up to service pack 3. For the last four months, XPs share in the market is holding steady around 55%. Vista's share is dropping as fast as Win7 is climbing. At this rate, Vista will be retired before XP. Win7 32 bit will function on just 2 gig RAM but not very well. Your CPU is just too old and motherboard's RAM limit should be 2 gigs. XP is the best one for you. And backup your personal files, you will need to reinstall programs, do a clean install of XP, get it to service pack 3 and try to keep it on IE7.
And you probably only want free virus protection. Get MSE.
and you can also run an antimalware with it
There are many Sony Vaio VGN AR models. Just let it scan your system to verify how much RAM the motherboard can handle. You really want at least 2 gigs of RAM in todays world. And at least 4 gigs RAM if on Win7 64 bit but motherboard needs to have at least a 4 gig RAM limit.
I just looked at one of those models on crucial.com, about $25 for a one gig RAM chip, odds are you will need to buy two of them and place the old ones in a box and stick it in a dark dry place. You might need them sometime. I used a macaroni and cheese box for my old chips.