I cannot move them onto the C: partition due to a lack of space and conflicts with steam.
Most likely because the registry of the game install is missing. You could reinstall the game. You can still install it to the D:\ drive though. Its a good idea to backup any registry information prior to a reinstall of Windows or use a image backup with all that data saved.

http://dl.dropbox.com/u/26677509/dad_cpuz_spd.jpg
And does the information given there mean that I should get ECC as opposed to NON-ECC (If I can read CPUZ, it seems to say it is ECC) or doesn't it matter? I have looked over ebuyer and I can't seem to find any PC2-5300 ECC so was considering going with something like http://www.ebuyer.com/91121-kingston-1gb-ddr2-667mhz-pc2-5300-memory-cl5-1-8v-kvr667d2n5-1g or http://www.ebuyer.com/106114-crucial-1gb-ddr2-667mhz-pc2-5300-memory-non-ecc-unbuffered-cl5-lifetime-warranty-ct12864aa667. (The UK dell site has excessive prices, like twice the price of ebuyer)
I think reliability is the key feature wanted over speed, and IIRC Green had a lower spin speed. Is there any noticable benifit in terms of relability? If there isn't much benifit I will just go for the cheaper blue (or any other recomendations?)
EDIT: Done some research. As far as I can work out, as long as you go for a harddrive from a big manufaturer then reliablity is much of a muchness. Sound about right?
All the RAM must be either ECC or Non-ECC, you cannot mix and match. ECC memory is more expensive in general. If it's difficult to find the correct modules you can always buy from cruical direct. It seems they are about 3GBP more expensive.
Here is a 2GB kit of the memory spec. you need (DDR2-5300 1.8v CL 5 ECC Unbuffered) : http://www.crucial.com/uk/store/mpartspecs.aspx?mtbpoid=36406F35A5CA7304
The Caviar Green and the Caviar Blue tiers have the same reliability. Caviar Green has a lower RPM to save power.
If reliability is paramount then I would check out the Western Digital RE4 (and RE4-GP) tiers. RE4 is the enterprise tier hard drives and RE4-GP is the "green" lower power version.
However, the Caviar Blue most likely is what you are looking for.