Hi Steve. 

Well, I don't actually need upgrades, in that everything works perfectly for the things I want to do.  However, because my OS is no longer supported, I don't get patches for security issues, etc, and can't use an up-to-date version of FF, which, apparently, can create vulnerabilities.

In technical terms, my machine would be capable of running Snow Leopard, which I could buy on a disc for £30-40 or so and then install.  However, I still wouldn't get any updates as SL is no longer receiving support by Apple.  I might be able to get a newer version of FF using it, but for how long?  I think the money would be better put towards an iPad instead (which would do 90% of what I want to do), as I would always be playing catch-up on this laptop.

I will still use it for some things, eg flash games, cos I can't play those on an iPad.