One word. RAM. Ok, that's technically three but I'm not being picky.
You need at least 512mb of RAM for the editor to really work. If you have a computer that has an onboard graphics card, then you won't really have the full amount of RAM to play with.
Therefore, I think a minimum of 768 or something should be specified. But hey... Who am I?!
At the end of the day, if you have less than 512mb of RAM, it's clear what you need to do:
<LI>Read the nice little prompt when you load up the editor which tells you you should have 512mb of RAM.
<LI>Buy more RAM.