Before getting into back-ups, here's the link to all the patches:
http://thesims2.ea.com/update/?pid=Help_patchesYou should probably do a quick run-though of the wiki's section on back-ups:
http://www.sims2wiki.info/wiki.php?title=Game_Help:Back_Upsbut here's a really condensed version:
Open My Documents--EA Games.
Right-click on The Sims 2 folder.
Choose Copy (or if Copy is not an option in the right-click menu, use either Control-C or Edit--Copy to copy the folder and all of its contents).
If, during the copy, you get an alert box asking if you are sure you want to copy something, click 'Yes To All.'
Go back to My Documents and create a new folder (you can name it whatever you wish) and open that newly-made folder.
Click inside that folder to 'set' the cursor, the either click Edit--Paste or use Control-V to paste the copy of the entire The Sims 2 folder.
This will take some time to finish, dependent on how large your copied folder is - it can certainly take a half-hour or more in some cases.
If, during the paste, you get an alert box asking if you are sure you want to paste something, click 'Yes To All.'
Once done, you'll have a copy of the pre-BV folder and can use that copy to replace a damaged or corrupted folder should that ever occur AND should you later decide to uninstall BV - the copy, if used as a replacement, will pick up the game exactly where it was when you did the back-up; that is one reason why periodic back-ups are recommended, to keep them current with your gameplay.
If you are happy with BV after it is installed and you've played it, I'd also recommend doing a separate fresh back-up of the BV-impacted The Sims 2 file to have on hand in case your with-BV game goes phffft at any time.