i recommend taking a look at a linux distribution that has a live cd. many different distributions have this as a feature of there install. a live cd allows you to try a linux installation without making any changes to your windows installation. while the speed might be slower the functionality should be there for you to try and see if you like it.
i recommend taking a look at the following distributions and feel free to ask any questions here in the forums
what a live cd will do for you is to see if the problem is with the laptop or with windows. if the live cd runs without freezeing than the problem is with windows. if the problem persists even on the live cd then you have a problem with hardware
if you have a hardware problem then next easiest step to start looking into this would be to test the memory. many live cds have a memory testing program called memtest86 already on them. i know for a fact ubuntu does but i'm sure others do as well.
good luck, i used to have an a65 as well and it was a great laptop.