backups are easy: I copy everything in the "The Sims 2" folder (my computer/my documents/EA Games/The Sims 2) and paste it into a new folder somewhere else on my computer. (it's not necessary to copy the Downloads folder if you have a lot there, but if you want to be sure that everything is there if you have to re-install the game, you should back up this too)
you can also save those files to an external harddrive or a cd or something like that.
the backup will only work with the EP's you have installed when you did the backup, so if you install a new EP/SP afterwards, you must remember to uninstall them for the backup to work.
to put in the backup, you remove all the current files in the folder mentioned above, and then copy/paste the backup into the empty folder.
PATCHES: you can find patches over at the official site
http://www.thesims2.ea.comI think one of the site modders had a list over what to install first and last when it came to EP's versus patches. I don't know where I found it, but it was written by one of the site modders
BeosBoxBoyINTEEN: the info about inteen is on the inteen site.
INSIM: there's both a FAQ area, a support manual, and a detailed explanation about the entire thing in the insim-mod area.