Answer to: What is causing sparkplugs to foul out?Make sure you check the spacing on your plugs in addition to checking to make sure they're not covered in oil or dirty in general. This rule goes for even the plugs that are pre-measured spacing. Other then that check your distributer cap and also spark plug wires if you keep having spark problems (also depending on your vehicle that type of spark plug wires can cause issues if they're not using tolerances that are equal to OEM).
Answer to: Upgrade Hard drivethe HDD is pretty easy to install - after you work your way threw the tear down the iMacs (majority of them) use just a standard SATA 3.5" HDD. (also the 20" and 24" depending on your model are pretty much the same with just more screws really - as for the tear down well....for my first one i used the tear down from here - ifixit.com - so just make sure you have a print out if this is your first tear down the reference is good to have so that you don't break anything or miss any screws). Back to the HDDs I think you can go up to the 1TB hdd without having any issues with the system's bios. I have upgraded 3 iMacs' hdds and all 3 they had no problem (oh side note - make sure you reconnect the heat sensor on the hdd, otherwise you can get false overheating alerts - i don't know if older iMacs have them but mine did). Once you install the new hdds and reconstruct the iMac with all of it's million screws, you can either simply run the OS Restore Disks or if you want to just image the hdd you can use the program S...