If you have sims living on the lot and you want to keep your house furnished,
you'll need the stay things shrub from SimLogical
http://www.simlogical.com/sl/Sims2Pages/Sims2_MovingHouse.htmDrop it in your downloads folder.
Place it on your lot and click on it.
Select the option you want to use from the pie menu.
Then you can go into neighborhood view, move your sims to the family bin
and package the lot and it
should be packaged as furnished.
Once you have packaged the lot, quit the game. Go to
C:\Documents and Settings\YOUR USER NAME\My Documents\EA Games\The Sims 2\PackagedLots
and
pull the packaged lot out of that folder and place it somewhere safe.
Now you'll have it to install as many times as you want.
This is a very important step- you don't want it to be accidentally lost or
overwritten.
I also suggest what gali said above- back everything up then you'll have it
just in case.
To get a fresh game without uninstalling/reinstalling-
Go into
C:\Documents and Settings\YOUR USER NAME\My Documents\EA Games
and pull out your Sims2 folder (if you have the space, place it on your
desktop and voila! instant back up.)
When you run the game, it will create a brand spanking new Sims2 folder for you, with the default neighborhoods/families/houses
Once you start up your game, go into your game options and enable custom
content. Quit the game and then you can install your house and at this point
you can install the custom content/downloads that you want to keep.
If you really don't care about your Saved Sims/Neighborhoods/Collections and
terrains- you can just delete those
from your back up copy.