A lot about computers?

I don't really like the Pentium D processor, because it consumes much more power, and therefore produces much more heat, than its successors.
More heat, in turn, means higher fan speed is necessary to keep it from overheating. So that means more NOISE from the fan as well. A better heatsink may help, but is expensive and can't be fitted if there's not enough space in a compact box.

Within your budget you may be able to score a CORE 2 Duo with similar specs. An i3 or higher is better but you'll be hard pressed to find one for that price.
If the copy of Win7 is genuine, then that's worth something too, so expect it to bump up the price a bit, especially now that XP is being exterminated. Lack of security updates is one thing, but for many folks it is the lack of driver support that force them to upgrade.
E.g. Hardware such as mother boards and printers/scanners are no longer supplied with XP drivers.

The same supplier has Core 2';s at £10 / 20 / 30 more - depending on the RAM & disk

The Pentium D is old technology, do not be swayed by it being 3.0GHZ (x2) - Core 2 duo is more powerful at a lower GHz, even the lowest Core 2 should be well above a Pentium D