Iceman 38 - I think DCNickie50 is asking for a size to be reserved for restore points. I know everyone's puter is different - but my restore points average around 50 MB - so if that's anything to go on - I would say 500 mb would be plenty.
That should give ya at least 5 restore points and that way - ya have more than one to fall back on if it is needed.
DCNickie50 - you also be sure to follow Iceman 38's excellent advice. Always create a restore point before u do anything major.
Oh yeah - In my opinion - never disable system restore - it has saved my butt a couple of times!