I'm old, and my mind is going.... (some would argue that not so much 'going', as 'went'.....) so, yeah, I needed to be reminded.
Your machine really isn't all that old, and you could probably do the powersupply, vid card, and later on, processor, and have a machine that would last your another year or three.... Or, you could set the money aside, and buy an all new machine, that would last you a year or three....... Granted, the newer machine would net you better performance, and, if you post how much ya wanna spend, what you would need, (just the tower? keyboard/monitor/mouse?) what country you are in, (Ireland???? just a guess....
) if you want pre-built, or, want to adventure out on your own, and try your own build...... folks here can give you some great suggestions...
Granted, upgrading your current machine to play oblivion would be cheaper RIGHT NOW..... but, I suspect you would have to pull another rabbit or two out of your hat for some upgrades to play games coming out later this year.