I was quite happy with XP myself.  However, Microsoft wanted to shut down XP when Vista was released.  Unfortunately for them, Vista was a piece of crap and businesses shunned it.  Windows 7 is supposed to have corrected the problems businesses had with Vista, and if that's the case, XP support will be shut down.

Moving from 32-bit to 64-bit is a biggie for me.  My old box had 4 GB of RAM, but any 32-bit operating system will only use 3 GB.  The addresses for the rest is beyond the capability of 32-bit I believe.  My new box has 8 GB of RAM which is now fully used with the 64-bit OS.

I've been running TS2 all all morning without any problems.  In fact I was having so much fun doing so, I forgot to add my tweaks to the Program Files.   

Google is your friend. Just type in Mod the Sims and it will give you results for it. Once there, in the download drop down menu, select Sims 3. When that loads, type the terms you are searching for and something ought to come up. Alternatively, look under game tools or mods. Have fun.

There is no simpe for TS3, But other tools out there. I know there's the postal package editor and s3pe Package Editor, You can find both of those on MTS. There was a saved game editor, But I can't find it know.