Thanks for the replies everyone. I'm trying to stretch out the lifespan of the pc in question because I'm saving up to buy a decent rig in the new year. I don't really want to spend more than £100-£150 absolute max (including any DDR2 RAM). Anything beyond that would be pointless for me.
For your budget of £150 that give you maximum upgrade potential if you consider upgrading next year aswell. Plus there would be not point you wasting money on DDR2 either as you'll only end up junking that on next upgrade.
And don't think I am an AMD fanboi, or that I think 775 is dead. I am far from that! I currently have a Pentium Dual Core myself and I made the mistake too of staying on 775.....
Stock cooling will be fine if your case airflow is good enough.
If you do want an aftermarket cooler, a good budget solution is the Arctic Cooler Freezer 7 Pro Rev 2, also from Scan priced at £16. I can recommend it, as it keeps my OC'd 775 E6700 at 4GHz cool enough and it supports 775/AM3 etc.