I checked the slots and the stick and there's definitely no evidence of burning or anything like that- both the sticks still look new. I put the good stick in the first slot (the one I thought was 'bad') and its was running ok. Though on task manager, I did notice that on idle, in that 'bad' slot, my good stick was using 1.3GB/1.4GB without any programs open. Whereas, it was using around 700MB when in the 'good' second slot. It the second slot however, it did crash about 2 hours into use, but I was using Photoshop, and on task manager, pretty much all my RAM was being used up with only the 2GB in, so it probably just froze due to it having no more memory to use. Vista doesnt seem to run too well, or too fast, on only 2gb. So now ive currently got the good stick in the 'bad' first slot, and the 'bad' stick in the second slot where it worked before (but this stick didn't work in the first slot) and I havent actually had any freezing (yet) but I am only using firefox. With both sticks in, it says I'm using 40% of my physical memory. Im not sure if it would be worth getting 4gb sticks, or at least 1 4GB stick to go with my good 2GB stick (even though they cost a leg). Basically, right now the sticks are in the other slot to what they were originally.
Though I'm just hoping thats the only problem, as my computer seems to be using a hefty amount of its CPU most of the time... I'll let you know if it crashes or anything, thanks