Hi there Tosh,
5711N0205W pretty much answered the first part of your question, but as for the second well the Semprons are the AMD equivalent of the Celeron, and make up the lower end of the CPU market. At the moment AMD Athlon 64s tend to make up the mid-range AMD market, with the higher clocked 64s, the FXs, and the X2s making up the higher end.
If you're looking to upgrade on a budget, then the best thing to go for would be an AMD Opteron 144 (Skt 939). These cost around £80-90, and I think the clock speed for that model is 1.8ghz or 2ghz. It would also involve getting a new motherboard. However, check this - the Opteron is basically a de-clocked FX-57 (which costs around £600-700) as it has the same core. It is also insanely overclockable, with speeds of upto 3ghz being hit on
stock cooling
. That's actually faster than an FX-57! So if you are upgrading and want to take the risk of overclocking, that's the best processor for the money
