Mac keeps freezing; what steps to take?

Hi,

I am using a Macbook Pro. With 10.5.8 OS.

Over the past few months my mac has gone through stages of freezing when online but eventually spreads to using anything on the Mac will create a freeze (iPlayer desktop, finder, PS, iTunes). I first started by uninstalling Chrome and using Safari instead. This worked for a few weeks. Then Safari stopped working. So I moved to Firefox. This worked for a few months. But low and behold Firefox started freezing the mac again. So now I am using Opera. But it is still freezing, not as bad as usual, but its only a matter of time before it is completely unusable.

When it freezes i get the beach ball but can usually move the cursor. The freeze starts randomly but especially when doing something 'difficult' like watching a video, or opening numerous tabs. Recently it even spread to BBC iPlayer desktop where I could not watch that offline or online as it would freeze the whole mac. It doesn't like iTunes either and wiped that library due to a crash corrupting files.

I have made numerous steps to counteract this such as Verifying and repairing disc permissions, downloading latest Flash (I can't download the absolute latest version as my mac OS doesn't support this). I have a feeling it might just be getting too old.

One last step I am contemplating is wiping it and restoring it to the factory settings. Would this help?

Many thanks for any help anyone can give me.